Display device and method for manufacturing the same

ABSTRACT

The present invention provides a method for manufacturing a highly reliable display device at a low cost with high yield. According to the present invention, a step due to an opening in a contact is covered with an insulating layer to reduce the step, and is processed into a gentle shape. A wiring or the like is formed to be in contact with the insulating layer and thus the coverage of the wiring or the like is enhanced. In addition, deterioration of a light-emitting element due to contaminants such as water can be prevented by sealing a layer including an organic material that has water permeability in a display device with a sealing material. Since the sealing material is formed in a portion of a driver circuit region in the display device, the frame margin of the display device can be narrowed.

BACKGROUND OF THE INVENTION 1. Field of the Present Invention

The present invention relates to a display device and a method formanufacturing the same.

2. Description of the Related Art

An EL element has a problem in that luminescence properties such asluminance or evenness of luminescence significantly deteriorate withtime, as compared with an early period. The low reliability is a factorin the limited practical application.

As one factor of worsening reliability, water or oxygen which intrudesinto the EL element from outside is given.

Accordingly, a display device having a structure for preventing thedeterioration of the EL element has been developed. In addition, thereis a method by which a sealing material is formed over an insulatorprovided with an EL element, and an enclosed space surrounded by acovering material and the sealing material is filled with a filler madeof resin or the like; therefore, the EL element is blocked off fromoutside (for example, Reference 1: Japanese Patent Application Laid-OpenNo. 2001-203076).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method formanufacturing a display device that is highly reliable and has superiorelectric characteristics, at a low cost with high yield withoutcomplicating a process and an apparatus for manufacturing the displaydevice.

According to the present invention, a step due to an opening in acontact is covered with an insulating layer to reduce the step, and isprocessed into a gentle shape. A wiring or the like is formed to be incontact with the insulating layer and thus the coverage of the wiring orthe like is enhanced. In addition, deterioration of a light-emittingelement due to contaminants such as water can be prevented by sealing alayer including an organic material that water permeability in a displaydevice with a sealing material. Since the sealing material is formed ina portion of a driver circuit region in the display device, the framemargin of the display device can be narrowed.

As for a display device to which the present invention can be applied,there is a light-emitting display device which includes a light-emittingelement having an organic material generating light-emission calledelectroluminescence (hereinafter, EL) or a medium having a mixture of anorganic material and an inorganic material between electrodes, and inwhich the light-emitting element is connected to a TFT.

One aspect of a display device according to the present invention is adisplay device including a pixel region; a connection region; asemiconductor layer including an impurity region in the pixel region; agate insulating layer over the semiconductor layer; a gate electrodelayer over the gate insulating layer; a first interlayer insulatinglayer over the gate electrode layer; a first opening that reaches theimpurity region in the gate insulating layer and the first interlayerinsulating layer; a source or drain electrode layer in the opening,wherein the source or drain electrode layer covers a portion of the gateelectrode layer with the first interlayer insulating layer therebetween;a second interlayer insulating layer over the source or drain electrodelayer and the first interlayer insulating layer, wherein the secondinterlayer insulating layer has a second opening that reaches the sourceor drain electrode layer, and the second opening is provided over thesource or drain electrode layer covering a portion of the gate electrodelayer with the first interlayer insulating layer therebetween; a firstelectrode layer in the second opening; a wiring layer provided over thefirst interlayer insulating layer in the connection region; the secondinterlayer insulating layer provided with a third opening, which reachesthe wiring layer, over the wiring layer, wherein an upper edge portionof the third opening is covered with an insulating layer; and a secondelectrode layer in the third opening to be in contact with theinsulating layer.

One aspect of a display device according to the present invention is adisplay device manufactured by forming a semiconductor layer includingan impurity region in a pixel region; forming a gate insulating layer ina connection region and over the semiconductor layer; forming a gateelectrode layer and a conductive layer over the gate insulating layer;forming a first interlayer insulating layer over the gate electrodelayer and the conductive layer, wherein the gate insulating layer andthe first interlayer insulating layer each have an opening that reachesthe impurity region; forming a source or drain electrode layer to coverthe first opening and a portion of the gate electrode layer; forming awiring layer to cover the conductive layer over the first interlayerinsulating layer; forming a second interlayer insulating layer over thefirst interlayer insulating layer, the wiring layer, the source or drainelectrode layer; forming a second opening that reaches the source ordrain electrode layer and a third opening that reaches the wiring layer,in the second interlayer insulating layer; forming a first electrodelayer in the second opening; forming an insulating layer to cover anupper edge portion of the third opening in the second interlayerinsulating layer and a portion of the first electrode layer; and forminga second electrode layer in the third opening to be in contact with theinsulating layer.

According to the present invention, a highly reliable display device canbe manufactured through a simplified process. Therefore, a displaydevice that exhibits high-precision and high-quality images can bemanufactured at a low cost with high yield.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B show a display device according to the presentinvention;

FIGS. 2A to 2D show a manufacturing method of a display device accordingto the present invention;

FIGS. 3A to 3C show a manufacturing method of a display device accordingto the present invention;

FIGS. 4A and 4B show a manufacturing method of a display deviceaccording to the present invention;

FIGS. 5A to 5C show a manufacturing method of a display device accordingto the present invention;

FIGS. 6A and 6B show a manufacturing method of a display deviceaccording to the present invention;

FIGS. 7A and 7B show a manufacturing method of a display deviceaccording to the present invention;

FIG. 8 shows a display device according to the present invention;

FIG. 9 shows a display device according to the present invention;

FIGS. 10A to 10C show a display device according to the presentinvention;

FIG. 11 shows a display device according to the present invention;

FIG. 12 shows a display device according to the present invention;

FIGS. 13A to 13D show a structure of a light-emitting element that canbe applied to the present invention;

FIG. 14 is an equivalent circuit of an EL display device that is shownin FIG. 15;

FIG. 15 is a top view for describing a display device according to thepresent invention;

FIGS. 16A to 16C are top views of a display device according to thepresent invention;

FIGS. 17A and 17B are top views of a display device according to thepresent invention;

FIG. 18 is a top view of a display device according to the presentinvention;

FIG. 19 shows a dropping method that can be applied to the presentinvention;

FIGS. 20A and 20B show an electronic device to which the presentinvention can be applied;

FIGS. 21A to 21D show an electronic device to which the presentinvention can be applied;

FIGS. 22A to 22I are SEM photographs of a sample manufactured in Example1;

FIGS. 23A to 23H are SEM photographs of a sample manufactured in Example1;

FIG. 24 shows an SIMS analysis result of a sample manufactured inExample 2;

FIG. 25 shows an SIMS analysis result of a sample manufactured inExample 2; and

FIG. 26 shows an SIMS analysis result of a sample manufactured inExample 2.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment Modes according to the present invention will hereinafter bedescribed with reference to the accompanying drawings. The presentinvention can be carried out in many different modes, and it is easilyunderstood by those skilled in the art that modes and details hereindisclosed can be modified in various ways without departing from thespirit and the scope of the present invention. It should be noted thatthe present invention should not be interpreted as being limited to thedescription of the embodiment modes to be given below. Note that thesame reference numerals are used for the same portions through alldrawings, and the description thereof is not repeated.

Embodiment Mode 1

A method for forming a thin film transistor in Embodiment Mode 1 isdescribed in detail with reference to FIGS. 1A to 6B.

In addition, FIG. 16A shows a top view of a structure of a display panelaccording to the present invention. A pixel portion 2701 in which pixels2702 are arranged in matrix, a scanning line input terminal 2703, and asignal line input terminal 2704 are formed over a substrate 2700 havingan insulating surface. The number of pixels may be provided according tovarious standards. The number of pixels of XGA may be 1024×768×3 (RGB),that of UXGA may be 1600×1200×3 (RGB), and that of a full-speck highvision may be 1920×1080×3 (RGB).

The pixels 2702 are arranged in matrix by intersecting a scanning lineextended from the scanning line input terminal 2703 with a signal lineextended from the signal line input terminal 2704. Each pixel 2702 isprovided with a switching element and a pixel electrode connectedthereto. A typical example of the switching element is a TFT. A gateelectrode side of a TFT is connected to the scanning line, and a sourceor drain side thereof is connected to the signal line; therefore, eachpixel can be controlled independently by a signal inputted from outside.

A TFT includes a semiconductor layer, a gate insulating layer, and agate electrode as main components. A wiring connected to source anddrain regions which are formed in the semiconductor layer accompaniesthereto. A top gate type in which a semiconductor layer, a gateinsulating layer and a gate electrode layer are sequentially arrangedfrom the substrate side, a bottom gate type in which a gate electrodelayer, a gate insulating layer and a semiconductor layer aresequentially arranged from the substrate side, and the like are known astypical structures of a TFT. However, any one of the structures may beapplied to the present invention.

FIG. 16A shows a structure of the display panel that controls a signalto be inputted into the scanning line and the signal line by theexternal driver circuit. Furthermore, a driver IC 2751 may be mounted ona substrate 2700 by a COG (Chip on Glass) method as shown in FIG. 17A.As another mounting mode, a TAB (Tape Automated Bonding) method may bealso employed as shown in FIG. 17B. The driver IC may be formed over asingle crystal semiconductor substrate, or may be formed of a circuithaving a TFT over a glass substrate. In FIGS. 17A and 17B, the driver IC2751 is connected to an FPC (flexible printed circuit) 2750.

When a TFT provided in a pixel is formed from a crystallinesemiconductor, a scanning line driver circuit 3702 may be formed to beintegrated over a substrate 3700 as shown in FIG. 16B. In FIG. 16B, apixel portion 3701 is controlled by an external driver circuit which isconnected to a signal line input terminal 3704 in the same manner asFIG. 16A. When a TFT provided in a pixel is formed from apolycrystalline (microcrystalline) semiconductor, a single crystallinesemiconductor or the like having high mobility, a scanning line drivercircuit 4702 and a signal line driver circuit 4704 can be formed to beintegrated over a substrate 4700 in FIG. 16C.

Over a substrate 100 having an insulating surface, a base film 101 a isformed to have a film thickness of 10 to 200 nm (preferably, from 50 to100 nm) using a silicon nitride oxide (SiNO) film by a sputteringmethod, a physical vapor deposition (PVD) method, a chemical vapordeposition (CVD) method such as a low-pressure CVD (LPCVD) method or aplasma CVD method, or the like, and a base film 101 b is stacked thereonto have a film thickness of 50 to 200 nm (preferably, from 100 to 150nm) using a silicon oxynitride (SiON) film as a base film. In thisembodiment mode, a plasma CVD method is used to form the base film 101 aand the base film 101 b. As the substrate 100, a glass substrate, aquartz substrate, a silicon substrate, a metal substrate such as SUSsubstrate, or a stainless substrate on the surface of which aninsulating film is formed, may be used. Additionally, a plasticsubstrate having heat-resistance which can withstand a processtemperature of this embodiment mode, or a flexible substrate like a filmmay also be used. As examples of the plastic substrate, substrates madefrom PET (polyethylene terephthalate), PEN (polyethylene naphthalate) orPES (polyeter sulfide) are given. A substrate made from synthetic resinsuch as acrylic can be used as the flexible substrate.

The base film can employ silicon oxide, silicon nitride, siliconoxynitride, silicon nitride oxide or the like, and may adopt a singlelayer, or a two-layer or three-layer stacked structure. Note that inthis specification, the silicon oxynitride is a substance which containsoxygen more than nitrogen in the composition ratio, and can be called asilicon oxide containing nitrogen. Similarly, the silicon nitride oxideis a substance which contains nitrogen more than oxygen in thecomposition ratio, and can be called a silicon nitride containingoxygen. In this embodiment mode, a silicon nitride oxide film is formedto be 50 nm thick using SiH₄, NH₃, N₂O, N₂ and H₂ as a reactive gas anda silicon oxynitride film is formed to be 100 nm thick using SiH₄ andN₂O as a reactive gas over a substrate. The thicknesses of the siliconnitride oxide film and the silicon oxynitride film to be stacked thereonmay be set 140 nm and 100 nm, respectively.

Subsequently, a semiconductor film is formed over the base film. Thesemiconductor film may be formed to have a thickness of from 25 to 200nm (preferably, from 30 to 150 nm) by a known method (sputtering, LPCVD,plasma CVD, or the like). In this embodiment mode, an amorphoussemiconductor film is crystallized by a laser to become a crystallinesemiconductor film, and the obtained crystalline semiconductor film ispreferably used.

An amorphous semiconductor (hereinafter also refereed to as “AS”)manufactured using a semiconductor material gas typified by silane orgermane with a vapor phase growth method or a sputtering method; apolycrystalline semiconductor that is formed by crystallizing theamorphous semiconductor utilizing light energy or thermal energy; asemi-amorphous (also referred to as microcrystalline, and hereinafteralso referred to as “SAS”) semiconductor; and the like can be used as amaterial for forming a semiconductor layer.

The SAS is a semiconductor with an intermediate structure between anamorphous and a crystal structure (including a single crystal and apolycrystal). This is a semiconductor having a third condition that isstable in terms of a free energy, and a crystalline region having ashort range order and lattice distortion. A crystalline region of 0.5 to20 nm can be observed at least in part of region in the film. Whensilicon is contained as the main component, Raman spectrum is shifted toa wavenumber side lower than 520 cm⁻¹. Diffraction peak of (111) and(220) to be caused from a crystal lattice of silicon are observed inX-ray diffraction. At least 1 atomic % or more of hydrogen or halogen iscontained to terminate a dangling bond. SAS is formed by carrying outgrow discharge decomposition (plasma CVD) on a silicide gas. In additionto SiH₄, Si₂H₆, SiH₂Cl₂, SiHC₃, SiCl₄, SiF₄, or the like can be used asthe silicide gas. In addition, F₂ or GeF₄ may be mixed. This silicidegas may be diluted with H₂ or H₂ and one or more of the rare gas elementof He, Ar, Kr, and Ne. A dilution ratio ranges from 2 to 1000 times. Apressure ranges approximately from 0.1 to 133 Pa, and a power frequencyranges from 1 to 120 MHz, preferably from 13 to 60 MHz. A substrateheating temperature is preferably 300° C. or less. A substrate heatingtemperature of 100 to 200° C. is possible. It is desirable that anatmospheric constituent impurity such as oxygen, nitrogen, or carbon is1×10²⁰ cm⁻³ or less as an impurity element in the film, specifically anoxygen concentration is 5×10¹⁹ cm⁻³ or less, preferably 1×10¹⁹ cm⁻³ orless. Further, a favorable SAS can be obtained by further promotinglattice distortion by adding a rare gas element such as helium, argon,krypton or neon to enhance stability. In addition, a SAS layer made froma silicide gas containing hydrogen may be stacked over a SAS layer madefrom a silicide gas containing fluorine as the semiconductor film.

An amorphous semiconductor is typified by hydrogenated amorphoussilicon, and a crystalline semiconductor is typified by polysilicon.Polysilicon (polycrystalline silicon) includes a so-called hightemperature polysilicon using polysilicon which is formed at atemperature of 800° C. or higher as a main material, a so-called lowtemperature polysilicon using polysilicon which is formed at atemperature of 600° C. or lower as a main material, a polysiliconcrystallized by being added with an element or the like which promotescrystallization, and the like. As described above, obviously, asemiamorphous semiconductor or a semiconductor which contains a crystalphase in a portion of the semiconductor layer can also be used.

When a crystalline semiconductor film is used as the semiconductor film,a known method (a laser crystallization method, a thermalcrystallization method, a thermal crystallization method using anelement promoting crystallization such as nickel, or the like) may beemployed as a method for manufacturing the crystalline semiconductorfilm. A microcrystalline semiconductor which is a SAS can becrystallized by being irradiated with laser light to enhance thecrystallinity. In the case where an element promoting crystallization isnot used, the hydrogen is released until the hydrogen concentrationcontained in an amorphous semiconductor film becomes 1×10²⁰ atoms/cm³ orless by heating the amorphous semiconductor film for one hour at atemperature of 500° C. in a nitrogen atmosphere before irradiating theamorphous semiconductor film with laser light. This is because anamorphous semiconductor film is damaged when the amorphous semiconductorfilm containing much hydrogen is irradiated with laser light. As a heattreatment for crystallization, a heating furnace, laser irradiation,light-irradiation from a lamp (lamp-annealing) and the like can beemployed. As the heating method, there is employed RTA method such asGRTA (Gas Rapid Thermal Anneal) or LRTA (Lamp Rapid Thermal Anneal).

Any method can be used for introducing a metal element into theamorphous semiconductor film without limitations as long as the methodis capable of making the metal element exist on the surface of or insidethe amorphous semiconductor film. For example, a sputtering method, aCVD method, a plasma treatment method (including a plasma CVD method),an adsorption method, or a method for applying a metal salt solution canbe employed. Among them, the method using a solution is simple and easyand advantageous in terms of easy concentration adjustment of the metalelement. It is preferable to form an oxide film by UV light irradiationin oxygen atmosphere, a thermal oxidation method, a treatment with ozonewater including a hydroxyl radical or hydrogen peroxide, or the like inorder to improve wettability of the surface of the amorphoussemiconductor layer and to spread the aqueous solution over the entiresurface of the amorphous semiconductor layer.

The semiconductor film is irradiated with the laser light having any oneof second to fourth harmonics of the fundamental wave from a continuouswave solid-state laser. Thus, a crystal having a large grain size can beobtained. For example, typically, it is preferable to use the secondharmonic (532 nm) or the third harmonic (355 nm) of an Nd:YVO₄ laser(fundamental wave 1064 nm). Specifically, the laser light emitted fromthe continuous wave YVO₄ laser is converted into the harmonic by anon-linear optical element to obtain laser light having the output ofseveral W or more. It is preferable to shape the laser light intorectangular or elliptical on an irradiated surface through an opticalsystem to irradiate the semiconductor film. The laser light needs tohave the power density of approximately 0.001 to 100 MW/cm² (preferably,from 0.1 to 10 MW/cm²). The scanning speed is set in the range ofapproximately 0.5 to 2000 cm/sec (preferably, 10 to 200 cm/sec) for theirradiation.

The shape of the laser beam is preferably linear. Thus, throughput canbe increased. In addition, the laser beam may be emitted with anincident angel θ (0°<θ<90°) with respect to the semiconductor film. Thisis because interference of laser beams can be prevented.

In this way, the laser beam is scanned relatively to the semiconductorfilm and thereby, laser irradiation can be conducted. In laserirradiation, a marker can be formed so as to overlap laser beams withgood accuracy or control the starting position and finishing position oflaser irradiation. The marker may be formed over the substrate at thesame time as the amorphous semiconductor film.

The laser may be a known continuous wave or pulsed gas laser,solid-state laser, copper vapor laser or gold vapor laser. As the gaslaser, there are an excimer laser, an Ar laser, a Kr laser, a He—Cdlaser and the like. As the solid-state laser, there are a YAG laser, aYVO₄ laser, a YLF laser, a YAlO₃ laser, a Y₂O₃ laser, a glass laser, aruby laser, an alexandrite laser, a Ti: Sapphire laser, and the like.

Moreover, a pulsed laser may be employed to conduct lasercrystallization. In this case, the pulse repetition rate is set to 0.5MHz or more. This frequency band is extremely higher than the frequencyband of several ten Hz to several hundred Hz, which is usually used. Itis said that it takes several ten to several hundred nanoseconds tocompletely solidify the semiconductor film after the semiconductor filmis irradiated with the pulsed laser light. When the pulsed laser lighthas the above described frequency band, it is possible to irradiate itwith next pulsed laser light after the semiconductor film is melted bythe previous pulsed laser light and before the semiconductor film issolidified. Therefore, the interface between the solid phase and theliquid phase can be continuously moved in the semiconductor film, andthe semiconductor film having a crystal grain continuously grown towardthe scanning direction is formed. Specifically, it is possible to forman aggregation of crystal grains each of which has a width of 10 to 30μm in the scanning direction and a width of approximately 1 to 5 μm in adirection perpendicular to the scanning direction. It is also possibleto form a semiconductor film having almost no crystal grain boundariesat least in the channel direction of a thin film transistor by forming asingle crystal grain long extended along the scanning direction.

The irradiation of the laser light may be conducted in an inert gasatmosphere such as a rare gas or nitrogen. This can suppress theroughness of a semiconductor surface by the irradiation of the laserlight and can reduce variations in a threshold value generated byvariations in the interface state density.

The amorphous semiconductor film may be crystallized by combining a heattreatment and laser light irradiation, or the heat treatment or thelaser light irradiation may be separately performed plural times.

In this embodiment mode, on the base film 101 b, an amorphoussemiconductor film is formed and crystallized to form a crystallinesemiconductor film. An amorphous silicon formed using SiH₄ and H₂ as areactive gas, is used as the amorphous semiconductor film. In thisembodiment mode, the base film 101 a, the base film 101 b and theamorphous semiconductor film are continuously formed by changingreactive gases while keeping vacuum (without breaking the vacuum) in thesame chamber at the same temperature of 330° C.

An oxide film formed on the amorphous semiconductor film is removed.Then, an oxide film is formed to be 1 to 5 nm thick by UV lightirradiation in an oxygen atmosphere, a thermal oxidation method, atreatment using ozone water including hydroxyl radical or hydrogenperoxide or the like. In this embodiment mode, Ni is used as the elementfor promoting crystallization. An aqueous solution including Ni acetateof 10 ppm is applied by a spin coating method.

In this embodiment mode, a heat treatment is conducted at 650° C. forsix minutes by a RTA method. Thereafter, an oxide film formed on thesemiconductor film is removed and the semiconductor film is irradiatedwith laser light. The amorphous semiconductor film is crystallized bythe above described crystallization to become a crystallinesemiconductor film.

When crystallization using a metal element is conducted, a getteringprocess is conducted so as to reduce or remove the metal element. Inthis embodiment mode, an amorphous semiconductor film is used as agettering sink to getter the metal element. An oxide film is formed onthe crystalline semiconductor film first by UV light irradiation in anoxygen atmosphere, a thermal oxidation method, a treatment using ozonewater including hydroxyl radical or hydrogen peroxide or the like. Theoxide film is preferably made thicker by a heat treatment. In thisembodiment mode, the oxide film is formed first and then, is madethicker by RTA at 650° C. for six minutes. Thereafter, an amorphoussemiconductor film of 30 nm thick is formed by a plasma CVD method (350W and 35 Pa in this embodiment mode).

After that, a heat treatment at 650° C. for six minutes is conducted byRTA to reduce or remove the metal element. The heat treatment may beconducted in a nitrogen atmosphere. The amorphous semiconductor filmserving as a gettering sink and the oxide film formed on the amorphoussemiconductor film are removed using hydrofluoric acid or the like,thereby obtaining a crystalline semiconductor film 102 in which themetal element is reduced or removed (FIG. 2A). In this embodiment mode,TMAH (tetramethyl ammonium hydroxide) is used for removing the amorphoussemiconductor film serving as a gettering sink.

The obtained semiconductor film may be doped with a minute amount of animpurity element (boron or phosphorus) in order to control a thresholdvalue of a thin film transistor. This doping of an impurity element maybe conducted to the amorphous semiconductor film before crystallization.If an impurity element is added into the amorphous semiconductor film,the impurity element can be activated by the heat treatment forcrystallization. In addition, defects or the like generated in dopingcan be improved.

The crystalline semiconductor film 102 is patterned using a mask. Inthis embodiment mode, the oxide film formed on the crystallinesemiconductor film 102 is removed and then a new oxide film is formed.Then, a photo mask is formed and patterning is conducted by aphotolithography method to form semiconductor layers 103 to 106.

An etching process in the patterning may be either plasma etching (dryetching) or wet etching; however, the plasma etching is suitable forprocessing a large substrate. A gas containing fluorine such as CF₄ orNF₃ or a gas containing chlorine such as Cl₂ or BCl₃ is used as theetching gas, and an inert gas such as He or Ar may be addedappropriately. In addition, if an etching process using atmosphericpressure discharge is applied, local discharge processing is possibleand a mask layer is not required to be formed over a whole surface ofthe substrate.

In the present invention, a conductive layer for forming a wiring layeror an electrode layer, a mask layer for forming a predetermined pattern,or the like may be formed by a method by which a pattern can beselectively formed, such as a droplet discharging method. By the dropletdischarging (jetting) method (also referred to as an inkjet methodaccording to the system thereof), a predetermined pattern (a conductivelayer, an insulating layer or the like) can be formed by selectivelydischarging (jetting) droplets of a composition prepared for a specificpurpose. In this case, a process for controlling wettability or adhesionmay be performed in a formation region. Additionally, a method fortransferring or drawing a pattern, for example, a printing method (amethod for forming a pattern, e.g., a screen printing or an offsetprinting) or the like can be used.

In this embodiment mode, a resin material such as an epoxy resin, anacrylic resin, a phenol resin, a novolac resin, a melamine resin, or anurethane resin is used as a mask. Alternatively, the mask may also bemade of an organic material such as benzocyclobutene, parylene, flareand polyimide having a light transmitting property; a compound materialformed by polymerization of a siloxane polymer or the like; acomposition material containing a water-soluble homopolymer and awater-soluble copolymer; and the like. In addition, a commerciallyavailable resist material containing a photosensitive agent may also beused. For example, it is possible to use a novolac resin, which is atypical positive resist, including a naphthoquinonediazide compound thatis a photosensitive agent; a base resin that is a negative resist,diphenylsilanediol, an acid generating material, and the like. Thesurface tension and the viscosity of any material are appropriatelyadjusted by controlling the solvent concentration, adding a surfactant,or the like, when a droplet discharging method is used.

The oxide film on the semiconductor layer is removed and then a gateinsulating layer 107 covering the semiconductor layers 103 to 105 isformed. An insulating film containing silicon is formed to be 10 to 150nm thick by a plasma CVD method or a sputtering method as the gateinsulating layer 107. A known material, e.g., an oxide material or anitride material of silicon typified by silicon nitride, silicon oxide,silicon oxynitride or silicon nitride oxide, may be formed for the gateinsulating layer 107, and the gate insulating layer 107 may have astacked-layer structure or a single layer structure. In this embodimentmode, a three-layer stacked structure of a silicon nitride film, asilicon oxide film and a silicon nitride film is used as the gateinsulating layer. In addition to that, a single layer of a siliconoxynitride film or a two-layer stacked structure may be employed.Preferably, a silicon nitride film having a dense film quality is used.A silicon oxide film having a thin thickness, 1 to 100 nm thick,preferably 1 to nm thick, more preferably 2 to 5 nm, may be formedbetween the semiconductor layer and the gate insulating layer. As themethod for forming the thin silicon oxide film, a thermal oxide film isformed by oxidizing a surface of the semiconductor region by GRTA, LRTAor the like, and thus the silicon oxide film having a thin filmthickness can be formed. Note that a reactive gas containing a rare gaselement such as argon may be mixed in an insulating film to be formed soas to form a dense insulating film with less gate-leak current at a lowtemperature.

Then, a first conductive film 108 of 20 to 100 nm thick is formed toserve as a gate electrode layer over the gate insulating layer 107 and asecond conductive film 109 of 100 to 400 nm thick is formed thereover(FIG. 2B). The first and second conductive films 108 and 109 can beformed by a known method such as sputtering, vapor deposition or CVD. Anelement selected from tantalum (Ta), tungsten (W), titanium (Ti),molybdenum (Mo), aluminum (Al), copper (Cu), chrome (Cr) and neodymium(Nd), or an alloy material or a compound material mainly containing theelements may be used to form the first and second conductive films 108and 109. A semiconductor film typified by a polysilicon film doped withan impurity element such as phosphorus or an AgPdCu alloy may be used asthe first and second conductive films 108 and 109. A three-layerstructure may be employed without being limited to the two-layerstructure, in which, for example, a tungsten film of 50 nm thick as thefirst conductive film, a aluminum-silicon (Al—Si) alloy film of 500 nmas the second conductive film, and a titanium nitride film of 30 nmthick as the third conductive film are formed sequentially. In the caseof the three-layer structure, tungsten nitride may be used instead ofthe tungsten film as the first conductive film, an aluminum-titanium(Al—Ti) alloy film may be used instead of the aluminum-silicon (Al—Si)film as the second conductive film, or a titanium film may be usedinstead of the titanium nitride film as the third conductive film.Alternatively, a single layer structure may be adopted. In thisembodiment mode, tantalum nitride (TaN) of 30 nm thick as the firstconductive film 106 and tungsten of 370 nm thick as the secondconductive film 107 are formed, respectively.

Then, masks 110 a, 110 b, 110 c, 110 d and 110 f are formed using resistby a photolithography method, and the first and second conductive films108 and 109 are patterned to form first gate electrode layers 121, 122,a conductive layer 123, first gate electrode layers 124 to 126, andconductive layers 111 to 116 (FIG. 2C). The first gate electrode layers121 an 122, the conductive layer 123, the first gate electrode layers124 to 126, and the conductive layers 111 to 116 can be etched to havedesired tapered shapes by appropriately adjusting an etching condition(electric power applied to a coil-shaped electrode layer, electric powerapplied to an electrode layer on a substrate side, electrode temperatureon a substrate side, or the like) by an ICP (Inductively Coupled Plasma)etching method. As the tapered shape, the angle or the like can becontrolled depending on the shape of the masks 110 a to 110 f. As theetching gas, a gas containing chlorine typified by Cl₂, BCl₃, SiCl₄,CCl₄, or the like, a gas containing fluorine typified by CF₄, CF₅, SF₆,NF₃, or the like, or O₂ can be appropriately used. In this embodimentmode, the second conductive film 109 is etched using an etching gasincluding CF₅, Cl₂ and O₂ and the first conductive film 108 is etchedcontinuously using an etching gas including CF₅ and Cl₂.

The conductive layers 111 to 116 are patterned using the masks 110 a,110 b, 110 c, 110 d, and 110 f. At this time, the conductive layers areetched with high selectivity of the second conductive film 109 formingthe conductive layer and the first conductive film 108 forming the firstgate electrode layer. By this etching, the conductive layers 111 to 116are etched to form the second gate electrode layers 131 and 132, theconductive layer 133, and the second gate electrode layers 134 to 136.In this embodiment mode, the third conductive layer also has a taperedshape, and the taper angle thereof is larger than those of the firstgate electrode layers 121 and 122, the conductive layer 123, the firstgate electrode layers 124 to 126. Note that the taper angle is an angleof a side face with respect to the surfaces of the first gate electrodelayer, the second gate electrode layer and the conductive layer.Therefore, if the taper angle is made large to be 90 degrees, theconductive layer has a vertical side face and the tapered shape is lost.In this embodiment mode, Cl₂, SF₆ and O₂ are used as an etching gas forforming the second gate electrode layer.

In this embodiment mode, the first gate electrode layers, the conductivelayers and the second gate electrode layers are formed to have taperedshapes and thus, the gate electrode layers with two layers both havetapered shapes. However, the present invention is not limited thereto,and only one layer of the to gate electrode layers may have a taperedshape, and the other thereof may have a vertical side face formed byanisotropic etching. As in this embodiment mode, the taper angels may bedifferent between the gate electrode layers to be stacked or may be thesame. The coverage of a film to be stacked thereover is enhanced due tothe taper shape and defects are reduced, thereby enhancing reliability.

Through the above-mentioned steps, a gate electrode layer 117 includingthe first gate electrode layer 121 and the second gate electrode layer131, and a gate electrode layer 118 including the first gate electrodelayer 122 and the second gate electrode layer 132 can be formed in aperipheral driver circuit region 204; a gate electrode layer 127including the first gate electrode layer 124 and the second gateelectrode layer 134, a gate electrode layer 128 including the first gateelectrode layer 125 and the second gate electrode layer 135, and a gateelectrode layer 129 including the first gate electrode layer 126 and thesecond gate electrode layer 136 can be formed in a pixel region 206; aconductive layer 130 including the conductive layer 123 and theconductive layer 133 can be formed in a connection region 205 (FIG. 2D).In this embodiment mode, the gate electrode layer is formed by dryetching; however, wet etching may be employed.

The gate insulating layer 107 is etched to some extent by the etchingprocess for forming the gate electrode layer, and thus the thicknessthereof is reduced in some cases.

In forming the gate electrode layer, a thin film transistor that canoperate at high speed can be formed by narrowing the width of the gateelectrode layer. Two methods for making the width in the channeldirection of the gate electrode layer thinner are shown hereinafter.

The first method is as follows: a mask for the gate electrode layer isformed and then the mask is slimed in the width direction by etching,ashing or the like to form a mask having a thinner width. The gateelectrode layer can be formed to have a thin shape by using the maskthat has been formed to have a thin shape.

The second method is as follows: a normal mask is formed and the gateelectrode layer is formed using the mask. The obtained gate electrodelayer is side-etched in the width direction to be more thinned. Thus,the gate electrode layer having a thin width can be formed finally.Through the above described steps, a thin film transistor having a shortchannel length can be formed later, and the thin film transistor thatcan operate at high speed can be manufactured.

An impurity element 151 imparting n-type conductivity is added using thegate electrode layers 117, 118, 127, 128 and 129 and the conductivelayer 130 as masks to form first n-type impurity regions 140 a, 140 b,141 a, 141 b, 142 a, 142 b, 142 c, 143 a and 143 b (FIG. 3A). In thisembodiment mode, phosphine (PH₃) (the composition ratio of P is 5%) isused as a doping gas containing an impurity element, and the doping isconducted under the conditions of gas flow rate of 80 sccm, beam currentof 54 μA/cm, accelerating voltage of 50 kV, and a dose amount of7.0×10¹³ ions/cm². Here, the first n-type impurity regions 140 a, 140 b,141 a, 141 b, 142 a, 142 b, 142 c, 143 a and 143 b are doped with theimpurity element imparting n-type conductivity such that the impurityelement is included in the regions to have the concentration of about1×10¹⁷ to 5×10¹⁸/cm³. In this embodiment mode, phosphorus (P) is used asthe impurity element imparting n-type conductivity.

In this embodiment mode, a region in which the impurity region overlapsthe gate electrode layer with the gate insulating layer therebetween isreferred to as Lov region, while a region in which the impurity regiondoes not overlap the gate electrode layer with the gate insulating layertherebetween is referred to as Loff region. In FIGS. 3A to 3C, theimpurity regions are shown by a portion without hatching and a portionwith hatching. This does not mean that the portion without hatching isnot doped with the impurity element, but this is made for easilyunderstanding that the concentration distribution of the impurityelement in the regions reflects masks or doping conditions. Note thatthis is true in the other drawings in this specification.

Masks 153 a, 153 b, 153 c and 153 d covering the semiconductor layer103, a portion of the semiconductor layer 105 and the semiconductorlayer 106 are formed. An impurity element 152 imparting n-typeconductivity is added using the masks 153 a, 153 b, 153 c and 153 d andthe gate electrode layer 132 as masks to form second n-type impurityregions 144 a, 144 b, third n-type impurity regions 145 a, 145 b, secondn-type impurity regions 147 a, 147 b, 147 c, and third n-type impurityregions 148 a, 148 b, 148 c, 148 d. In this embodiment mode, PH₃ (thecomposition ratio of P is 5%) is used as a doping gas containing animpurity element, and the doping is conducted under the conditions ofgas flow rate of 80 sccm, beam current of 540 μA/cm, acceleratingvoltage of 70 kV, and a dose amount of 5.0×10¹⁵ ions/cm². Here, thesecond n-type impurity regions 144 a, 144 b are doped with the impurityelement imparting n-type conductivity such that the impurity element isincluded into the regions to have the concentration of about 5×10¹⁹ to5×10²⁰/cm³. The third impurity regions 145 a, 145 b are formed toinclude the impurity element imparting n-type conductivity in theconcentration almost equal to or slightly higher than those of the thirdn-type impurity regions 148 a, 148 b, 148 c, 148 d. In addition, achannel forming region 146 is formed in the semiconductor layer 104, andchannel forming regions 149 a, 149 b are formed in the semiconductorlayer 105.

The second n-type impurity regions 144 a, 144 b, 147 a, 147 b, 147 c areeach a high concentration n-type impurity region and serve as a sourceor a drain. On the other hand, the third n-type impurity regions 145 a,145 b, 148 a, 148 b, 148 c 148 d are each a low concentration impurityregion, that is, an LDD (Lightly Doped Drain) region. The n-typeimpurity regions 145 a, 145 b are overlapped with the first gateelectrode layer 122 with the gate insulating layer 107 therebetween, andthus it is a Lov region, which relieves an electric field in aneighborhood of a drain and can control deterioration of on-current byhot carriers. As a result, a thin film transistor that can operate athigh speed can be formed. On the other hand, the third n-type impurityregions 148 a, 148 b, 148 c and 148 d are formed in an Loff region thatis not overlapped with the gate electrode layers 127 and 128, and thusthe regions relieve an electric field in a neighborhood of a drain, andcan control deterioration due to hot carriers and can reduceoff-current. As a result, a highly reliable semiconductor device thatconsumes less power can be manufactured.

The masks 153 a, 153 b, 153 c, 153 d are removed and masks 155 a, 155 bcovering the semiconductor layers 103, 105 are formed. An impurityelement 154 imparting p-type conductivity is added using the masks 155a, 155 b, the gate electrode layers 117 and 129 as masks to form firstp-type impurity regions 160 a, 160 b, 163 a, 163 b and second p-typeimpurity regions 161 a, 161 b, 164 a, 164 b. In this embodiment mode,boron (B) is used as the impurity element. Diborane (B₂H₆) (thecomposition ratio of B is 15%) is used as a doping gas containing animpurity element, and the doping is conducted under the conditions ofgas flow rate of 70 sccm, beam current of 180 μA/cm, acceleratingvoltage of 80 kV, and a dose amount of 2.0×10¹⁵ ions/cm². Here, thefirst p-type impurity regions 160 a, 160 b, 163 a, 163 b, and the secondp-type impurity regions 161 a, 161 b, 164 a, 164 b are doped with theimpurity element imparting p-type conductivity such that the impurityelement is included into the regions to have the concentration of about1×10²⁰ to 5×10²¹/cm³. In this embodiment mode, the second p-typeimpurity regions 161 a, 161 b, 164 a, 164 b are formed to have aconcentration lower than those of the first p-type impurity regions 160a, 160 b, 163 a, 163 b in a self-alignment manner depending on theshapes of the gate electrode layers 117 and 129. A channel formingregion 162 is formed in the semiconductor layer 103, and a channelforming region 165 is formed in the semiconductor layer 106.

The second n-type impurity regions 144 a, 144 b, 147 a, 147 b, 147 c areeach a high concentration n-type impurity region and serve as a sourceor a drain. On the other hand, the second p-type impurity regions 161 a,161 b, 164 a, 164 b are each a low concentration impurity region, thatis, an LDD (Lightly Doped Drain) region. The second p-type impurityregions 161 a, 161 b, 164 a, 164 b are overlapped with the first gateelectrode layers 121 and 126 with the gate insulating layer 107therebetween, and thus it is a Lov region, which relieves an electricfield in a neighborhood of a drain and can control deterioration ofon-current due to hot carriers.

The masks 155 a and 155 b are removed by O₂ ashing or using a resistpeeling solution and the oxide film is also removed. After that, aninsulating film, so-called sidewall may be formed to cover the side ofthe gate electrode layer. The sidewall can be formed from an insulatingfilm containing silicon by a plasma CVD method or a low pressure CVDmethod (LPCVD).

A heat treatment, irradiation of intense light or laser irradiation maybe conducted to activate the impurity element. Plasma damage to the gateinsulating layer or to an interface between the gate insulating layerand the semiconductor layer may be recovered as well as the activation.

Thereafter, an interlayer insulating layer is formed to cover the gateelectrode layer and the gate insulating layer. In this embodiment mode,a stacked structure of the insulating film 167 and the insulating film168 is employed (FIG. 4A). A silicon nitride oxide film of 200 nm thickis formed as the insulating film 167, and a silicon oxynitride film of800 nm thick is formed as the insulating film 168 to be stacked. Inaddition, a three-layer stacked structure may be employed, for example,a silicon oxynitride film of 30 nm thick, a silicon nitride oxide filmof 140 nm thick and a silicon oxynitride film of 800 nm thick may bestacked to cover the gate electrode layer and the gate insulating layer.In this embodiment mode, the insulating films 167 and 168 are formedsequentially by plasma CVD in the same way as the base film. Theinsulating films 167 and 168 are not limited in particular, and may beformed of a silicon nitride film, a silicon nitride oxide film, asilicon oxynitride film or a silicon oxide film formed by sputtering orplasma CVD, and may have a single layer of another insulating filmcontaining silicon or a stacked structure of three-layer of otherinsulating films containing silicon.

Further, the step for hydrogenating the semiconductor layers isperformed by a heat treatment at a temperature of 300 to 550° C. for 1to 12 hours in a nitrogen atmosphere. This step is preferably performedat a temperature of 400 to 500° C. This step is a step for terminatingdangling bonds of the semiconductor layer due to hydrogen contained inthe insulating film 167 serving as the interlayer insulating layer. Inthis embodiment mode, the heat treatment is conducted at 410° C.

The insulating films 167 and 168 can be formed using a material selectedfrom aluminum nitride (AlN), aluminum oxynitride (AlON), aluminumnitride oxide having more nitrogen content than oxygen content (AlNO),aluminum oxide, diamond like carbon (DLC), and a nitrogen-containingcarbon film (CN) film and other substances containing an inorganicinsulating material. Further, siloxane resin may be employed. Thesiloxane resin is a resin containing Si—O—Si bond. Siloxane includes askeleton formed by the bond of silicon (Si) and oxygen (O), in which anorganic group containing at least hydrogen (such as an alkyl group oraromatic hydrocarbon) is included as a substituent. In addition, afluoro group may be used as the substituent. Further, a fluoro group andan organic group containing at least hydrogen may be used as thesubstituent. An organic insulating material may be employed, forexample, polyimide, acrylic, polyamide, polyimide amide, resist,benzocyclobutene or polysilazane can be used. A coated film formed by acoating method that can provide favorable flatness may be used.

Thereafter, contact holes (openings) that reach the semiconductor layerare formed in the insulating films 167 and 168 and the gate insulatinglayer 107 with a mask of resist. Etching may be conducted once ormultiple times depending on the selectivity of a material to be used. Inthis embodiment mode, first etching is conducted to remove theinsulating film 168, under a condition that the selectivity of theinsulating film 168 including silicon oxynitride and the insulating film167 including silicon nitride oxide and the gate insulating layer 107can be obtained. Next, the insulating film 167 and the gate insulatinglayer 107 are removed by second etching to form openings that reach thefirst p-type impurity regions 160 a, 160 b, 163 a, 163 b and the secondn-type impurity regions 144 a, 144 b, 147 a, 147 b, which are each asource region or a drain region. In this embodiment mode, the firstetching is wet etching and the second etching is dry etching. As anetchant for wet etching, a hydrofluoric acid based solution such as amixed solution of ammonium hydrogen fluoride and ammonium fluoride maybe used. As an etching gas, a gas containing chlorine typified by Cl₂,BCl₃, SiCl₄, CCl₄, or the like, a gas containing fluorine typified byCF₄, SF₆, NF₃, or the like, or O₂ can be appropriately used. An inertgas may be added into the etching gas to be used. As the inert elementto be added, one or a plurality of elements selected from He, Ne, Ar,Kr, and Xe can be used.

A conductive film is formed to cover the openings and then etched toform source or drain electrode layers 169 a, 169 b, 170 a, 170 b, 171 a,171 b, 172 a, 172 b and a wiring 156 electrically connected to a portionof each source or drain region. These source or drain electrode layerscan be formed by forming a conductive film by a PVD method, a CVDmethod, a vapor deposition method, or the like, and etching theconductive film into a desired shape. In addition, the conductive layercan be formed selectively at a predetermined position by a dropletdischarging method, a printing method, an electroplating method, or thelike. Moreover, a reflow method or a damascene method can be used. As amaterial for the source or drain electrode layers, a metal such as Ag,Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Si, Ge, Zr,or Ba; an alloy of the metal; or a metal nitride of the metal is used.In addition, a stacked structure of these materials may be adopted. Inthis embodiment mode, titanium (Ti) of 100 nm thick, an aluminum-silicon(AL-Si) alloy of 700 nm thick, and titanium (TI) of 200 nm thick arestacked and patterned into a desired shape.

Through the above described steps, an active matrix substrate can bemanufactured, in which a p-channel thin film transistor 173 having ap-type impurity region and an n-channel thin film transistor 174 havingan n-type impurity region are formed in the Lov regions in theperipheral driver circuit region 204; a conductive layer 177 is formedin a connection region; a multi channel type n-channel thin filmtransistor 175 having n-type impurity region is formed in the Loffregion and a p-channel thin film transistor 176 having a p-type impurityregion is formed in the Lov region in the pixel region 206 (FIG. 4B).

The active matrix substrate can be used for a light-emitting devicehaving a self light-emitting element, a liquid crystal display devicehaving a liquid crystal element, and other display devices. In addition,the active matrix substrate can also be used for various processorstypified by CPU (central processing unit), and a semiconductor devicesuch as a card having an ID chip.

The thin film transistor may have a single-gate structure having onechannel forming region, a double-gate structure having two channelforming regions or a triple-gate structure having three channel formingregions without being limited to this embodiment mode. The thin filmtransistor in the peripheral driver circuit region may also have any oneof a single-gate structure, a double-gate structure and a triple-gatestructure.

The present invention is not limited to the method for forming a TFTshown in this embodiment mode. The present invention can be applied to atop-gate type (planar type), a bottom-gate type (inversely staggeredtype), a dual-gate type having two gate electrode layers arranged aboveand below of a channel region with gate insulating films interposedtherebetween, and other structures.

Next, insulating films 180 and 181 are formed as second interlayerinsulating layers (FIG. 5A). FIGS. 5A to 5C show manufacturing steps ofa display device, in which a region 201 to be cut out by scribing, anexternal terminal connection region 202 to be attached with an FPC, awiring region 203 that is a region for leading a wiring in theperipheral portion, a peripheral driver circuit region 204, a connectionregion 205, and a pixel region 260 are provided. Wirings 179 a and 179 bare formed in the wiring region 203, and a terminal electrode layer 178to be connected with an external terminal is formed in the externalterminal connection region 202.

The insulating films 180 and 181 can be formed using a material selectedfrom silicon oxide, silicon nitride, silicon oxynitride, silicon nitrideoxide, aluminum nitride (AlN), aluminum oxynitride (AlON), aluminumnitride oxide having more nitrogen content than oxygen content (AlNO),aluminum oxide, diamond like carbon (DLC), a nitrogen-containing carbon(CN) film, a PSG (phosphorus glass), a BPSG (boron phosphorus glass), analumina film and other substances containing an inorganic insulatingmaterial. Further, a siloxane resin may be employed. A photosensitive ornon-photosensitive organic insulating material may be employed, forexample, polyimide, acrylic, polyamide, polyimide amide, resist orbenzocyclobutene, polysilazane, or a low-k material that is lowdielectric can be used.

In this embodiment mode, a silicon oxynitride film of 200 nm thick isformed as the insulating film 180 by a CVD method. The insulating film181 is preferably formed by a coating method such as spin coating,because a layer that is superior in heat-resistance, insulative propertyand planarity is needed as the interlayer insulating film forplanarizing, A coated film of siloxane resin is used as the material ofthe insulating film 181 in this embodiment mode. The film after bakingcan be referred to as a silicon oxide film containing an alkyl group(SiOx) (x=1, 2 . . . ). This silicon oxide film containing an alkylgroup (SiOx) can withstand a heat treatment of 300° C. or more.

Dip coating, spraying coating, a doctor knife, a roll coater, a curtaincoater, a knife coater, a CVD method, a vapor deposition method or thelike can be used for forming the insulating films 180 and 181. Inaddition, the insulating films 180 and 181 may be formed by a dropletdischarging method. A material solution can be saved when the dropletdischarging method is adopted. A method capable of transferring ordrawing a pattern like the droplet discharging method, for example, aprinting method (a method by which a pattern is formed, such as screenprinting or offset printing), or the like can also be used.

As shown in FIG. 5B, openings are formed in the insulating films 180 and181 that serve as the second interlayer insulating layer. The insulatingfilms 180 and 181 are required to be etched widely in the connectionregion 205, the wiring region 203, the external terminal connectionregion 202, the region to be cut out 201 and the like. However, the areaof the opening in the pixel region 206 is still smaller than that in theconnection region 205 or the like, and becomes minute. Therefore, amargin of etching condition can be widened by conducting aphotolithography process for forming the opening in the pixel region anda photolithography process for forming the opening in the connectionregion. Consequently, the yield can be improved. Contact holes in thepixel region can be formed with high accuracy by widening the margin ofthe etching condition.

Specifically, openings having large areas are formed in the insulatingfilm 180 and 181 formed partially in the connection region 205, thewiring region 203, the external terminal connection region 202, theregion to be cut out 201 and a portion of the peripheral driver circuitregion 204. Thus, masks are formed to cover the insulating film 180 and181 formed in the pixel region 206, and in parts of the connectionregion 205 and the peripheral driver circuit region 204. Parallel-plateRIE (reactive ion etching) system or ICP etching system can be used foretching. Note that the time for etching may be set such that the wiringlayer or the first interlayer insulating layer is over etched. Variationin film thickness within the substrate and variation in etching rate canbe reduced by setting it such that the wiring layer or the firstinterlayer insulating layer is over etched. In this way, the opening182, 183 are formed in the connection region 205 and the externalterminal connection region 202, respectively.

As shown in FIG. 5B, a minute opening, in other words, a contact hole,is formed in the insulating films 180 and 181 in the pixel region 206(FIG. 5C). At this time, a mask is formed to cover the pixel region 206,a portion of the connection region 205, a portion of the peripheraldriver circuit region 204 and the pixel region 206. The mask is a maskfor forming the opening in the pixel region 206, and is provided with aminute opening in a desired position thereof. A resist mask can, forexample, be used as the mask.

The insulating films 180 and 181 are etched with the parallel-plate RIE(reactive ion etching) system. Note that the time for etching may be setsuch that the wiring layer or the first interlayer insulating layer isover etched. Variation in film thickness within the substrate andvariation in etching rate can be reduced by setting it such that thewiring layer or the first interlayer insulating layer is over etched.

An ICP system may be used for the etching system. Through the abovedescribed steps, an opening 184 that reaches the source or drainelectrode layer 172 a is formed in the pixel region 206. In the presentinvention, the source or drain electrode layer 172 a is formed to coverthe gate electrode layer 126 having a large total thickness in which alarge number of thin films are stacked in the thin film transistor 176,with the insulating films 167 and 168 therebetween. Thus, since theopening 184 is not required to be formed deep, the process for formingthe opening can be shortened, and thus the controllability can beenhanced. In addition, an electrode layer to be formed in the openingcan be formed with favorable coverage and thus reliability can beenhanced, because the electrode layer does not need to widely cover theopening having a large angle.

This embodiment mode describes the case in which the insulating films180 and 181 are etched using the mask covering the connection region205, the wiring region 203, a portion of the external terminalconnection region 202, the region to be cut out 201, and a portion ofthe peripheral driver circuit region 204 and having a desired opening inthe pixel region 206. However, the present invention is not limitedthereto. For example, the area of the opening in the connection region204 is large, and thus the amount to be etched is large. The openinghaving a large area may be etched plural times. If an opening that isdeeper than other openings is formed, etching may be conducted pluraltimes similarly.

In this embodiment mode, the formation of the openings in the insulatingfilms 180 and 181 are conducted multiple times as shown in FIGS. 5B and5C; however, only one-time etching may be conducted. In this case, anICP system is used to conduct etching with ICP power of 7000 W, biaspower of 1000 W, pressure of 0.8 Pa, with the use of CF₄ of 240 sccm andO₂ of 160 sccm as the etching gas. The bias power is preferably 1000 to4000 W. At this time, an advantageous effect that the process can besimplified is obtained, because one-time etching is enough for formingthe opening.

Then, a first electrode 185 (also referred to as a pixel electrode) isformed to be in contact with the source or drain electrode layer 172 a.The first electrode layer serves as an anode or a cathode, and may beformed with a film made from an element selected from Ti, TiN,TiSi_(X)N_(Y), Ni, W, WSi_(X), WN_(X), WSi_(X)N_(Y), NbN, Cr, Pt, Zn,Sn, In and Mo, an alloy material or a compound material mainlycontaining the element; or a stacked structure of such films to have atotal thickness of 100 to 800 nm.

In this embodiment mode, a light-emitting element is used as a displayelement, and light emitted from the light-emitting element is extractedfrom the first electrode layer 185 side. Thus, the first electrode layer185 is light-transmitting. A transparent conductive film is formed asthe first electrode layer 185 and etched into a desired shape, therebyobtaining the first electrode layer 185. Indium tin oxide containingsilicon oxide (also referred to as ITSO), zinc oxide, tin oxide, indiumoxide or the like may be used for the first electrode layer 185 used inthe present invention. In addition, a transparent conductive film suchas an indium zinc oxide alloy in which indium oxide is mixed with zincoxide (ZnO) of 2 to 20% can be used. A titanium nitride film or atitanium film may be used for the first electrode layer 185 in additionto the above described transparent conductive films. In this case, afterthe transparent conductive film is formed, a titanium nitride film or atitanium film is formed to have such a thickness that can transmit light(preferably about 5 to 30 nm thick). In this embodiment mode, ITSOcontaining indium tin oxide and silicon oxide are used as the firstelectrode layer 185. In this embodiment mode, the ITSO film is formed tobe 185 nm thick by sputtering using, as a target, indium tin oxide mixedwith silicon oxide (SiO₂) of 1 to 10% and setting the flow of Ar gas at120 sccm; O₂ gas, 5 sccm; pressure, 0.25 Pa; and power, 3.2 kW. Thefirst electrode layer 185 may be cleaned and polished by CMP or by usinga porous material such as polyvinyl alcohol so that the surface thereofis planarized. In addition, after polishing with a CMP method,ultraviolet ray irradiation, an oxygen plasma treatment, or the like maybe carried out on the surface of the first electrode layer 185.

A heat treatment may be performed after forming the first electrodelayer 185. With the heat treatment, water included in the firstelectrode layer 185 is released. Accordingly, degasification or the likeis not generated from the first electrode layer 185. Even when a lightemitting material which is easily deteriorated by water is formed overthe first electrode layer, the light emitting material is notdeteriorated; therefore, a highly reliable display device can bemanufactured. In this embodiment mode, ITSO is used for the firstelectrode layer 185, and it remains an amorphous state even when bakingis performed, unlike ITO (indium tin oxide) which is crystallized bybeing baked. Hence, ITSO has higher planarity than ITO, andshort-circuit with a cathode is not easily generated even when a layercontaining an organic compound is thin.

Next, an insulator (an insulating layer) 186 (also, referred to as abank, a partition wall, a wall, an embankment or the like) covering anedge portion of the first electrode layer 185 and the source or drainelectrode layer is formed (FIG. 6B). Insulators 187 a, 187 b are formedin the external terminal connection region 202 in the same step. In thisembodiment mode, acrylic is used for the insulator 186. When theinsulator 186 is formed from the same material in the same process asthe insulating film 181, manufacturing cost can be reduced. Further, thecost can also be reduced by commonly using a coating apparatus or anetching apparatus.

The insulator 186 is formed with an inorganic insulating material suchas silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride, or other inorganic insulatingmaterials, or acrylic acid, methacrylic acid, or a derivative thereof, aheat resistant high molecular weight compound such as polyimide, anaromatic polyamide, or polybenzimidazole or siloxane resin. Aphotosensitive or nonphotosensitive material such as acrylic orpolyimide may be used. The insulator 186 preferably has a shape in whicha radius curvature changes continuously. Accordingly, the coverage of anelectroluminescent layer 188 and a second electrode layer 189 which areformed over the insulator 186 is enhanced.

In the connection region 205, the insulator 186 is formed to cover upperedge portions of the insulating films 180 and 181 on the side face ofthe opening 182. The upper edge portions of the insulating films 180 and181 that have been processed to have steps by patterning have rapidsteps. Therefore, the coverage of the second electrode layer 189 to beformed thereon is not favorable. As in the present invention, the stepsin the periphery of the opening is covered with the insulator 186 tosmooth the steps, thereby enhancing the coverage of the second electrodelayer 189 to be stacked thereon. In the connection region 205, a wiringlayer to be formed in the same process and from the same material as thesecond electrode layer is electrically connected to the wiring layer156. In this embodiment mode, the second electrode layer 189 is directlyin contact with the wiring layer 156 to be electrically connected;however, may be electrically connected via another wiring.

It is preferable to perform deaeration by carrying out vacuum heatingbefore forming an electroluminescent layer (a layer including an organiccompound) 188 to further improve reliability. For example, it isdesirable to perform a heat treatment at 200 to 400° C., preferably, 250to 350° C. in a low pressure atmosphere or inert atmosphere beforeevaporating an organic compound material in order to eliminate the gascontained in the substrate. It is preferable to form theelectroluminescent layer 188 by a vapor deposition method or a dropletdischarging method in a low pressure without being exposed to theatmosphere. According to the heat treatment, water contained in oradhering to a conductive film, which is to be the first electrode layer,or the insulating layer (bank) can be released. The heat treatment canbe conducted with the above-mentioned heat treatment when vacuum is keptand the substrate can be transferred within a vacuum chamber, and theabove-mentioned heat treatment may be performed once after forming theinsulating layer (bank). Here, when the interlayer insulating film andthe insulating layer (bank) are formed of a substance having high heatresistance, a step for enhancing reliability by heat treatment can besufficiently performed.

The electroluminescent layer 188 is formed over the first electrodelayer 185. Note that although only one pixel is shown in FIGS. 1A and1B, electroluminescent layers corresponding to each color of R (red), G(green) and B (blue) are separately formed in this embodiment mode. Inthis embodiment mode, as the electroluminescent layer 188, materialswhich show luminescence of each color of red (R), green (G) and blue (B)are selectively formed by a vapor deposition method using a vapordeposition mask for each, or the like. The materials, which showluminescence of each color red (R), green (G) and blue (B), can be alsoformed by a droplet discharging method (a low molecular or highmolecular weight material, or the like) and, in this case, separatecoating of RGB can be carried out without using a mask, which ispreferable.

Next, the second electrode layer 189 formed of a conductive film isprovided over the electroluminescent layer 188. As the second electrodelayer 189, a material with a low work function (Al, Ag, Li, Ca, or analloy thereof, such as MgAg, MgIn, AILi, CaF₂, or CaN) may be used. Inthis manner, a light-emitting element 190 including the first electrodelayer 185, the electroluminescent layer 188 and the second electrodelayer 189 is formed.

In the display device according to this embodiment mode shown in FIGS.1A and 1B, light emitted from the light emitting element 190 is emittedin the direction shown by the arrow in FIG. 1B from the side of thefirst electrode layer 185.

It is effective to provide a passivation film 191 so as to cover thesecond electrode layer 189. The passivation film 191 is formed of aninsulating film containing silicon nitride, silicon oxide, siliconoxynitride (SiON), silicon nitride oxide (SiNO), aluminum nitride (AlN),aluminum oxynitride (AlON), aluminum nitride oxide (AlNO) of whichnitrogen content is larger than oxygen content, aluminum oxide, diamondlike carbon (DLC), or a carbon film containing nitrogen (CN), and asingle layer of the insulating film or a stacked layer of the films canbe used. In addition, a siloxane resin may be used.

In this case, it is preferable to use a film with good coverage as thepassivation film, and a carbon film, a DLC film, in particular, iseffective. Since a DLC film can be formed at temperatures ranging from aroom temperature to 100° C. or less, it can be easily formed even overthe electroluminescent layer 188 with low heat resistance. A DLC filmcan be formed by a plasma CVD method (typically, an RF plasma CVDmethod, a microwave CVD method, an electron cyclotron resonance (ECR)CVD method, a hot-filament CVD method, or the like), a combustion flamemethod, a sputtering method, an ion beam vapor deposition method, alaser vapor deposition method, or the like. As a reactive gas to be usedfor deposition, a hydrogen gas and a hydrocarbon based gas (for example,CH₄, C₂H₂, C₆H₆ or the like) are used and ionized by glow discharge, andthen deposition is carried out with accelerative collision of ions witha cathode to which a negative self-bias is applied. In addition, the CNfilm may be formed by using C₂H₄ gas and N₂ gas as a reactive gas. A DLCfilm has high blocking effect to oxygen and thus can control oxidationof the electroluminescent layer 188. Therefore, a problem that theelectroluminescent layer 188 oxidizes can be prevented during asubsequent sealing step.

FIG. 18 is a top view of a pixel region of the display device formed inthis embodiment mode. In FIG. 18, a pixel 2702 includes thin filmtransistors 501, 502, a capacitor 504, a light-emitting element 503, agate wiring layer 506, a source or drain wiring layer 505 and a powersupply line 507.

The light emitting element is sealed by bonding the substrate 100 wherethe light emitting element 190 is formed to a sealing substrate 195 witha sealing material 192 (FIGS. 1A and 1B). Water is prevented fromentering through a cross-section by the sealing material; therefore, thelight emitting element is prevented from deteriorating, which leads tothe higher reliability of the display device. As the sealing material192, a visible light curing, ultraviolet curing or thermosetting resinis preferably used. For example, an epoxy resin such as a bisphenol Aliquid resin, a bisphenol A solid resin, a resin containing bromo-epoxy,a bisphenol F resin, a bisphenol AD resin, a phenol resin, a cresolresin, a novolac resin, a cyclic aliphatic epoxy resin, an epibis epoxyresin, a glycidyl ester resin, a glycidyl amine resin, a heterocyclicepoxy resin, or a modified epoxy resin can be used. Note that a regionsurrounded with the sealing material may be filled with a filler 193,and nitrogen or the like may be encapsulated therein by sealing thelight emitting element in a nitrogen atmosphere. The filler 193 does notnecessarily have light-transmitting properties, since a bottom emissiontype is employed in this embodiment mode. In the case of a structure inwhich light is extracted through the filler 193, the filler needs tohave light-transmitting properties. Typically, a visible light curing,ultraviolet curing, or thermosetting epoxy resin may be used. Throughthe above described steps, a display device having a display functionusing a light emitting element in this embodiment mode is completed.Further, the filler in a liquid state may be dropped and can fill theinside of the display device.

A dropping method (a method by which a filler is injecting by beingdropped) using a dispenser method is described with reference to FIG.19. The dropping method in FIG. 19 includes a control device 40, animaging means 42, a head 43, a filler 33, markers 35, 45, a barrierlayer 34, a sealing material 32, a TFT substrate 30, and an oppositesubstrate 20. A closed loop is formed by the sealing material 32, andthe filler 33 is dropped thereinto once or plural times from the head43. If the viscosity of the filler material is high, the filler isdischarged continuously and attached to a formation region with thefiller extended. On the other hand, if the viscosity of the fillermaterial is low, the filler is discharged intermittently and dropped asshown in FIG. 19. The barrier layer 34 may be provided so as to preventthe sealing material 32 from reacting with the filler 33. Then, thesubstrates are attached in vacuum, and then cured by ultraviolet rays tobe filled with the filler. When a hygroscopic material such as a dryingagent is used as the filler, a further absorption effect of water isobtained and deterioration of an element can be prevented.

A drying agent is provided in an EL display panel so as to preventdeterioration of an element due to water. In this embodiment mode, thedrying agent is provided in a concave portion formed to surround thepixel region in the sealing substrate, so as not to hinder thinning. Inaddition, a drying agent is also provided in a region corresponding to agate wiring layer, and the area of water absorption is large, whichleads to high absorption efficiency. Further, since the drying agent isprovided on the gate wiring layer that does not emit light for itself,light-extraction efficiency is not reduced.

Note that this embodiment mode shows the case in which thelight-emitting element is sealed with the glass substrate. The sealingtreatment is a treatment to protect the light emitting element fromwater. Therefore, any of a method by which a light emitting element ismechanically sealed with a cover material, a method by which a lightemitting element is sealed with a thermosetting resin or an ultravioletcuring resin, and a method by which a light emitting element is sealedwith a thin film of such as a oxide or nitride of a metal or the likehaving high barrier capabilities, can be used. As for the covermaterial, glass, ceramics, plastic, or metal can be used. However, whenlight is emitted to the cover material side, the cover material needs tohave light-transmitting properties. Enclosed space is formed byattaching the cover material to the substrate over which theabove-mentioned light emitting element is formed with a sealing materialsuch as a thermosetting resin or an ultraviolet curing resin and then bycuring the resin with a heat treatment or an ultraviolet irradiationtreatment. It is also effective to provide a hydroscopic materialtypified by barium oxide in the enclosed space. The hydroscopic materialmay be provided on the sealing material or over a bank or in theperipheral part thereof so as not to block light emitted from the lightemitting element. Further, it is also possible to fill the space betweenthe cover material and the substrate over which the light emittingelement is formed with a thermosetting resin or an ultraviolet curingresin. In this case, it is effective to add a hydroscopic materialtypified by barium oxide in the thermosetting resin or the ultravioletcuring resin.

In this embodiment mode, in the external terminal connection region 202,an FPC 194 is connected to the terminal electrode layer 178 with ananisotropic conductive layer 196, so as to make an electrical connectionto the outside.

In this embodiment mode, the display device includes the above-mentionedcircuits. However, the present invention is not limited thereto. As aperipheral driver circuit, an IC chip may be mounted by a COG method orTAB method mentioned above. Additionally, a single or a plurality ofgate line driver circuits and source line driver circuits may be used.

In the display device of the present invention, a method for driving ascreen is not specifically limited, for example, a dot sequentialdriving system, a line sequential driving system, a plane sequentialdriving system, or the like may be employed. Typically, the linesequential driving system is employed, and a time division gray-scaledriving system or an area gray-scale driving system may be utilized asneeded. The video signal to be inputted into a source line of thedisplay device may be either an analog signal or a digital signal, andthe driver circuit or the like may be designed corresponding to thevideo signal as needed.

Further, in a display device using a digital video signal, there are twokinds of driving systems in which a video signal inputted into a pixelis one with constant voltage (CV) and in which a video signal inputtedinto a pixel is one with constant current (CC). Further, as for thedriving system using a video signal with constant voltage (CV), thereare two kinds of systems in which voltage applied to a light emittingelement is constant (CVCV), and in which current applied to a lightemitting element is constant (CVCC). In addition, as for the drivingsystem using a video signal with constant current (CC), there are twokinds of systems in which voltage applied to a light emitting element isconstant (CCCV), and in which current applied to a light emittingelement is constant (CCCC).

According to the present invention, a highly reliable display device canbe manufactured through a simplified process. Therefore, a displaydevice that exhibits high-precision and high-quality images can bemanufactured at a low cost with high yield.

Embodiment Mode 2

Embodiment Mode according to the present invention is described withreference to FIGS. 7A to 9. Embodiment Mode 2 describes an example inwhich a second interlayer insulating film is not formed in the displaydevice manufactured in Embodiment Mode 1. Therefore, the description ofthe same portions and the portions having the same function is omitted.

As shown in Embodiment Mode 1, thin film transistors 173 to 176, aconductive layer 177, and insulating films 167 and 168 are formed over asubstrate 100. A source or drain electrode layer to be connected to asource or drain region of a semiconductor layer is formed in each thinfilm transistor. A first electrode layer 395 is formed to be in contactwith a source or drain electrode layer 172 b in the thin film transistor176 provided in a pixel region 206 (FIG. 7A).

The first electrode layer 395 serves as a pixel electrode, and may beformed from the same material in the same process as the first electrodelayer 185 in Embodiment Mode 1. In this embodiment mode, light isextracted through the first electrode layer as in Embodiment Mode 1, andthus ITSO that is a transparent conductive film is used as the firstelectrode layer 395 and patterned.

An insulator 186 is formed to cover an edge portion of the firstelectrode layer 395 and the thin film transistors (FIG. 7B). Acrylic isused for the insulator 186 in this embodiment mode. Anelectroluminescent layer 188 is formed over the first electrode layerand a second electrode layer 189 is stacked thereover to obtain alight-emitting element 190. The second electrode layer 189 iselectrically connected to a wiring layer 156 in a connection region 205.A terminal electrode layer 178 is bonded to an FPC 194 by an anisotropicconductive layer 196 in an external terminal connection region 202. Apassivation film 191 is formed to cover the second electrode layer 189.The substrate 100 is attached to a sealing substrate 195 by a sealingmaterial 192, and a filler 193 fills a display device (FIG. 8).

In the display device shown in FIG. 9, the first electrode layer 395 canselectively formed over the insulating film 168 before forming thesource or electrode layer 172 b to be connected to the thin filmtransistor 176. In this case, the source or drain electrode layer 172 bis connected to the first electrode layer 395 by stacking the source ordrain electrode layer 172 b over the first electrode layer. When thefirst electrode layer 395 is formed before forming the source or drainelectrode layer 172 b, the first electrode layer 395 can be formed in aflat region; therefore, there are advantages of good coverage, good filmformation conditions, and good planarity since it is possible tosufficiently conduct a polishing treatment such as CMP.

According to the present invention, a highly reliable display device canbe manufactured through a simplified process. Therefore, a displaydevice that exhibits high-precision and high-quality images can bemanufactured at a low cost with high yield.

Embodiment Mode 3

Embodiment Mode according to the present invention is described withreference to FIGS. 10A to 10C. Embodiment Mode 3 describes an example inwhich a gate electrode layer of a thin film transistor has a differentstructure in the display device manufactured in Embodiment Mode 1.Therefore, the description of the same portions and the portions havingthe same function is omitted.

FIGS. 10A to 10C show a display device that is being formed in amanufacturing process and corresponds to the display device shown inFIG. 4B described in Embodiment Mode 1.

In FIG. 10A, thin film transistors 273, 274 are formed in a peripheraldriver circuit region 214, a conductive layer 277 is formed in aconnection region 215, and thin film transistors 275, 276 are formed ina pixel region 216. A gate electrode layer of a thin film transistor inFIG. 10A has a stacked structure of two conductive films, in which anupper gate electrode layer is patterned to have a width narrower than alower gate electrode layer. The lower gate electrode layer has a taperedshape but the upper gate electrode layer does not have a tapered shape.In this manner, the gate electrode layer may have a tapered shape or theangle in the side thereof may substantially be vertical, in other words,the gate electrode layer may not have a tapered shape.

In FIG. 10B, thin film transistors 373, 374 are formed in the peripheraldriver circuit region 214, a conductive layer 377 is formed in theconnection region 215, and thin film transistors 375, 376 are formed inthe pixel region 216. The gate electrode layer of the thin filmtransistor in FIG. 10B also has a stacked structure of two conductivefilms and the upper and lower gate electrode layers have a continuoustapered shape.

In FIG. 10C, thin film transistors 473, 474 are formed in the peripheraldriver circuit region 214, a conductive layer 477 is formed in theconnection region 215, and thin film transistors 475, 476 are formed inthe pixel region 216. The gate electrode layer of the thin filmtransistor in FIG. 10C has a single layer structure and has a taperedshape. Like this, the gate electrode layer may have a single layerstructure.

As described above, the gate electrode layer can have various structuresdepending on the structure and shape thereof. Thus, the obtained displaydevice can have various structures. When an impurity region in thesemiconductor layer is formed in a self alignment manner with a gateelectrode layer as a mask, the structure of the impurity region or aconcentration distribution is varied depending on the structure of thegate electrode layer. If a thin film transistor is designed inconsideration of the above, the thin film transistor having desiredfunctions can be obtained.

This embodiment mode can be freely combined with Embodiment Modes 1 and2.

Embodiment Mode 4

A display device having a light emitting element can be manufactured byapplying the present invention. Light is emitted from the light emittingelement in bottom emission, top emission, or dual emission. In thisembodiment mode, examples of a dual emission type and a top emissiontype will be described with reference to FIG. 11 and FIG. 12.

A display device shown in FIG. 12 includes an element substrate 1300;TFTs 1355, 1365 and 1375; a first electrode layer 1317; anelectroluminescent layer 1319; a second electrode layer 1320; atransparent conductive film 1321; a filler 1322; a sealing material1325; a gate insulating layer 1310; insulating films 1309, 1311 to 1313;an insulator 1314; a sealing substrate 1323; a wiring layer 1375; aterminal electrode layer 1381; an anisotropic conductive layer 1382; andan FPC 1383. The display device includes a region to be cut out 221, anexternal terminal connection region 222, a wiring region 223, aperipheral driver circuit region 224 and a pixel region 226. The filler1322 can be formed by a dropping method using a composition in liquidform as in the case of the dropping method in FIG. 19. The lightemitting display device is sealed by attaching the element substrate1300 provided with the filler to the sealing substrate 1323 by a dropmethod.

The display device shown in FIG. 12 is a dual emission type, and has astructure in which light is emitted in directions indicated by arrows,namely, to the both sides of the element substrate 1300 and the sealingsubstrate 1323. In this embodiment mode, a transparent conductive filmis formed and etched to have a desired shape to form the first electrodelayer 1317. A transparent conductive film can be used as the firstelectrode layer 1317. In addition to the transparent conductive film, atitanium nitride film or a titanium film may be used as the firstelectrode layer 1317. In this case, a titanium nitride film or atitanium film is formed to have a film thickness which allows totransmit light (preferably, approximately from 5 to 30 nm) after formingthe transparent conductive film. In this embodiment mode, ITSO is usedas the first electrode layer 1317.

Then, a second electrode layer 1320 formed with a conductive film isformed over the electroluminescent layer 1319. As the second electrodelayer 1320, a material having a low work function (Al, Ag, Li, Ca; analloy thereof such as MgAg, Mgln, AlLi; or a compound thereof such asCaF₂, or CaN) may be used. In the display device shown in FIG. 12, ametal thin film with a thinned film thickness (MgAg: a film thickness of10 nm) as the second electrode layer 1320, and ITSO having a filmthickness of 100 nm as the transparent conductive film 1321 are stackedso that light can be transmitted. As the transparent conductive film1321, a film similar to the above-mentioned first electrode layer 1317can be used.

A display device shown in FIG. 11 is a one-side emission type, and has astructure in which top emission is performed in a direction indicated byan arrow. The display device shown in FIG. 11 includes an elementsubstrate 1600, TFTs 1655, 1665 and 1675, a reflective metal layer 1624,a first electrode layer 1617, an electroluminescent layer 1619, a secondelectrode layer 1620, a transparent conductive film 1621, a filler 1622,a sealing material 1625, a gate insulating layer 1610, insulating films1611 to 1613 and 1609, an insulator 1614, a sealing substrate 1623, awiring layer 1675, a terminal electrode layer 1681, an anisotropicconductive layer 1682 and an FPC 1683. In the display device in FIG. 11,the insulating layer stacked over the terminal electrode layer 1681 isetched to be removed. In this manner, the structure in which a moisturepermeable insulating layer is not provided in the periphery of theterminal electrode layer can enhance the reliability. In addition, thedisplay device includes a region to be cut out 231, an external terminalconnection region 232, a wiring region 233, a peripheral driver circuitregion 234 and a pixel region 236. In this case, in the dual emissiontype display device shown in FIG. 12, the reflective metal layer 1624 isformed under the first electrode layer 1617. The first electrode layer1617 functioning as an anode, which is formed of a transparentconductive film, is formed over the reflective metal layer 1624. As themetal layer 1624, it may be at least reflective; therefore, Ta, W, Ti,Mo, Al, Cu or the like may be used. It is preferable to use a substancehaving high reflectivity in a visible light range, and in thisembodiment mode, a TiN film is used. The present invention is applied tothe insulating layer 1609 and the bank 1614; thus, the display devicecan provide high definition display without display unevenness owing tothe uniform thickness distribution and the high planarity of theinsulating 1609.

The second electrode layer 1620 formed of a conductive film is providedover the electroluminescent layer 1619. As the second electrode layer1620, a material having a low work function (Al, Ag, Li, Ca; an alloythereof such as MgAg, MgIn, AILi; or a compound thereof such as CaF₂, orCaN) may be used so as to be used as a cathode. In this embodiment mode,a metal thin film with thinned film thickness as the second electrodelayer 1620 (MgAg: a film thickness of 10 nm) and ITSO having a filmthickness of 110 nm as the transparent conductive film 1621 are stackedso that light can be transmitted.

A mode of a light emitting element which can be applied in thisembodiment mode is shown in FIG. 13A to 13D. The light emitting elementhas a structure in which an electroluminescent layer 860 is interposedbetween a first electrode layer 870 and a second electrode layer 850.The materials of the first electrode layer and the second electrodelayer are required to be selected considering the work functions. Thefirst electrode layer and the second electrode layer can be either ananode or a cathode depending on the pixel structure. In this embodimentmode, in the case where a driving TFT has a p-channel conductivity, thefirst electrode layer may preferably serve as an anode and the secondelectrode layer may serve as a cathode. Since the driving TFT has ann-channel conductivity, the first electrode layer may preferably be usedas a cathode and the second electrode layer may preferably be used as ananode.

FIGS. 13A and 13B show the case where the first electrode layer 870 isan anode and the second electrode layer 850 is a cathode. Theelectroluminescent layer 860 preferably has a structure in which an HIL(hole injection layer)/HTL (hole transport layer) 804, an EML (lightemitting layer) 803, an ETL (electron transport layer)/EIL (electroninjection layer) 802, and a second electrode layer 850 are stacked inorder from the side of the first electrode layer 870. FIG. 13A shows astructure in which light is emitted from the first electrode layer 870which includes an electrode layer 805 having a light-transmittingconductive oxide material, and the second electrode layer has astructure in which an electrode layer 801 containing an alkali metal oran alkaline earth metal such as LiF or MgAg and an electrode layer 800made of a metal material such as aluminum are stacked in order from theside of the electroluminescent layer 860. FIG. 13B shows a structure inwhich light is emitted from the second electrode layer 850, and in whichthe first electrode layer includes an electrode layer 807 made of ametal such as aluminum or titanium, or a metal material containing sucha metal and nitrogen of concentration in stoichiometric proportion orless, and the second electrode layer 806 made of a conductive oxidematerial containing silicon oxide at a concentration of 1 to 15 atomic%. The second electrode layer is constituted by an electrode layer 801containing an alkali metal or an alkaline earth metal such as LiF orMgAg and an electrode layer 800 made of a metal material such asaluminum from the side of the electroluminescent layer 860; each layeris formed to have a thickness of 100 nm or less to transmit light; thus,the light can be emitted from the second electrode layer 850.

FIGS. 13C and 13D show the case where the first electrode layer 870 is acathode and the second electrode layer 850 is an anode. Theelectroluminescent layer 860 preferably has a structure in which an EIL(electron injection layer)/an ETL (electron transport layer) 802, an EML(light emitting layer) 803, an HTL (hole transport layer)/HIL (holeinjection layer) 804, and the second electrode layer 850 which is ananode are stacked in order from the cathode side. FIG. 13C shows astructure in which light is emitted from the first electrode layer 870.The first electrode layer 870 includes an electrode layer 801 containingan alkali metal or an alkaline earth metal such as LiF or MgAg and anelectrode layer 800 made of a metal material such as aluminum from theside of the electroluminescent layer 860; each layer is formed to have athickness of 100 nm or less to transmit light; thus, the light can beemitted from the first electrode layer 870. The second electrode layerincludes the second electrode layer 806 made of a conductive oxidematerial containing silicon oxide at a concentration of 1 to 15 atomic %and an electrode layer 807 made of a metal such as aluminum or titanium,or a metal material containing such a metal and nitrogen ofconcentration in stoichiometric proportion or less, from the side of theelectroluminescent layer 860. FIG. 13D shows a structure in which lightis emitted from the second electrode layer 850. The first electrodelayer 870 includes an electrode layer 801 containing an alkali metal oran alkaline earth metal such as LiF or MgAg and an electrode layer 800made of a metal material such as aluminum from the side of theelectroluminescent layer 860; the first electrode layer 870 is formedthick enough to reflect the light produced in the electroluminescentlayer 860. The second electrode layer 850 includes an electrode layer805 made of a light-transmitting conductive oxide material. Theelectroluminescent layer may have a single layer structure or a mixedstructure instead of a stacked structure.

As the electroluminescent layer, materials each displaying luminescenceof red (R), green (G), and blue (B) are selectively formed by a vapordeposition method using a vapor deposition mask, respectively. Thematerials (low molecular weight materials or high molecular weightmaterials or the like) each displaying luminescence of red (R), green(G), and blue (B) can be formed by a droplet discharging method in thesame manner as a color filter. This case is preferable since RGB can beseparately colored without using masks.

In the case of the top emission type, when ITO or ITSO havinglight-transmitting property is used as the second electrode layer,BzOs-Li in which Li is added to benzoxazole derivatives (BzOs) or thelike can be used. Alq₃ doped with a dopant corresponding to respectiveluminescent colors of R, G, and B (DCM or the like for R, and DMQD orthe like for G) may be used for the EML, for example.

Note that the electroluminescent layer is not limited to theabove-mentioned materials. For example, hole injection properties can beenhanced by co-evaporating an oxide such as molybdenum oxide (MoOx: x=2to 3) and α-NPD or rubrene instead of using CuPc or PEDOT. An organicmaterial (including a low molecular weight material or a high molecularweight material) or a composite material of an organic material and aninorganic material can be used as the material of the electroluminescentlayer. A material forming the light emitting element will be describedbelow in detail.

As a substance having high electron transport properties among chargeinjection transport materials, for example, a metal complex having aquinoline skeleton or a benzoquinoline skeleton such astris(8-quinolinolato) aluminum (Alq₃), tris(4-methyl-8-quinolinolato)aluminum (Almq₃), bis (10-h ydroxybenzo[h]-quinolinato) beryllium(BeBq₂), bis (2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum(BAIq), and the like can be given. As a substance having high holetransport properties, for example, an aromatic amine compound (in otherwords, a compound having the bond of benzene ring-nitrogen) such as4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (α-NPD),4,4′-bis[N-(3-methylphenyl)-N-phenyl-amino]-biphenyl (TPD),4,4′,4″-tris(N,N-diphenyl-amino)-triphenylamine (TDATA), or4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine (MTDATA)can be used.

As a substance having high electron injection properties among chargeinjection transport materials, a compound of an alkali metal or analkaline earth metal such as lithium fluoride (LiF), cesium fluoride(CsF), or calcium fluoride (CaF₂) can be given. In addition to this, itmay be a mixture of a substance having high electron transportproperties such as Alq₃ and an alkaline earth metal such as magnesium(Mg).

As a substance having high hole injection properties among chargeinjection transport materials, for example, a metal oxide such asmolybdenum oxide (MoOx), vanadium oxide (VOx), ruthenium oxide (RuOx),tungsten oxide (WOx), or manganese oxide (MnOx) is used. In addition,phthalocyanine (H₂Pc) or a phthalocyanine compound such as copperphthalocyanine (CuPc) can be used.

The light emitting layer may perform color display by providing eachpixel with light emitting layers having different emission wavelengthranges. Typically, a light emitting layer corresponding to each color ofR (red), G (green), or B (blue) is formed. On this occasion, colorpurity can be improved and a pixel portion can be prevented from havinga mirror surface (reflection) by providing the light emission side ofthe pixel with a filter which transmits light of an emission wavelengthrange. By providing a filter, a circularly polarizing plate or the likethat is conventionally required can be omitted, and further, the loss oflight emitted from the light emitting layer can be eliminated. Further,change in hue, which occurs when a pixel portion (display screen) isobliquely seen, can be reduced.

Various materials can be used for the light emitting material. As a lowmolecular weight organic light emitting material,4-dicyanomethylene-2-methyl-6-[2-(1,1,7,7-tetramethyl-9-julolidyl)ethenyl]-4H-pyran;(DCJT);4-dicyanomethylene-2-t-butyl-6-[2-(1,1,7,7-tetramethyljulolidine-9-yl-ethenyl)]-4H-pyran;(DCJTB); periflanthene;2,5-dicyano-1,4-bis[2-(10-methoxy-1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]benzene;N,N′-dimethylquinacridon (DMQd); coumarin 6; coumarin 545T;tris(8-quinolinolato)aluminum (Alq₃); 9,9′-bianthryl;9,10-diphenylanthracene (DPA); 9,10-bis(2-naphthyl)anthracene (DNA); andthe like can be used. Another substance can also be used.

On the other hand, a high molecular weight organic light emittingmaterial is physically stronger than a low molecular weight material andis superior in durability of the element. In addition, a high molecularweight organic light emitting material can be formed by coating;therefore, the element can be relatively manufactured easily. Thestructure of a light emitting element using a high molecular weightorganic light emitting material basically has the same structure as inthe case of using a low molecular weight organic light emittingmaterial, that is, a cathode, an organic light emitting layer, and ananode are stacked in order. However, a two-layer structure is employedin many cases when a light emitting layer using a high molecular weightorganic light emitting material is formed. This is because it isdifficult to form such a stacked structure as in the case of using a lowmolecular weight organic light emitting material. Specifically, thelight emitting element using a high molecular weight organic lightemitting material, has a structure of a cathode, a light emitting layer,a hole transport layer, and an anode in order.

The emission color is determined depending on a material forming thelight emitting layer; therefore, a light emitting element which displaysdesired luminescence can be formed by selecting an appropriate materialfor the light emitting layer. As a high molecular weightelectroluminescent material which can be used for forming a lightemitting layer, a polyparaphenylene-vinylene-based material, apolyparaphenylene-based material, a polythiophene-based material, or apolyfluorene-based material can be used.

As the polyparaphenylene vinylene-based material, a derivative ofpoly(paraphenylenevinylene) [PPV], for example,poly(2,5-dialkoxy-1,4-phenylenevinylene) [RO-PPV];poly(2-(2′-ethyl-hexoxy)-5-methoxy-1,4-phenylenevinylene) [MEH-PPV];poly(2-(dialkoxyphenyl)-1,4-phenylenevinylene) [ROPh-PPV]; and the likecan be used. As the polyparaphenylene-based material, a derivative ofpolyparaphenylene [PPP], for example, poly(2,5-dialkoxy-1,4-phenylene)[RO-PPP]; poly(2,5-dihexoxy-1,4-phenylene); and the like can be used. Asthe polythiophene-based material, a derivative of a derivative ofpolythiophene [PT], for example, poly(3-alkylthiophene) [PAT];poly(3-hexylthiophen) [PHT]; poly(3-cyclohexylthiophen) [PCHT];poly(3-cyclohexyl-4-methylthiophene) [PCHMT];poly(3,4-dicyclohexylthiophene) [PDCHT];poly[3-(4-octylphenyl)-thiophene] [POPT];poly[3-(4-octylphenyl)-2,2bithiophene] [PTOPT]; and the like can beused. As the polyfluorene-based material, a derivative of polyfluorene[PF], for example, poly(9,9-dialkylfluorene) [PDAF];poly(9,9-dioctylfluorene) [PDOF]; and the like can be used.

When a high molecular weight organic light emitting material having holetransport properties is formed between an anode and a high molecularweight organic light emitting material having light emitting properties,hole injection properties from the anode can be enhanced. Generally, ahigh molecular weight organic light emitting material having holetransport properties which is dissolved in water with an acceptormaterial is applied by spin coating or the like. In addition, the highmolecular weight light emitting material having hole injectionproperties is insoluble in an organic solvent; therefore, it can beformed over the above-mentioned high molecular weight organic lightemitting material having light emitting properties. As the highmolecular weight organic light emitting material having hole transportproperties, a mixture of PEDOT and camphor sulfonic acid (CSA) thatserves as an acceptor material, a mixture of polyaniline [PANI] andpolystyrene sulfonic acid [PSS] that serves as an acceptor material, orthe like can be used.

The light emitting layer can be made to emit single color or whitelight. When a white light emitting material is used, color display canbe made possible by applying a structure in which a filter (a coloringlayer) which transmits light having a specific wavelength to the lightemitting side of a pixel is provided.

In order to form a light emitting layer that emits white light, forexample, Alq₃, Alq₃ partially doped with Nile red that is a red lightemitting colorant, Alq₃, p-EtTAZ, TPD (aromatic diamine) are stacked inorder by a vapor deposition method to obtain white light. In the casewhere an EL is formed by an application method using spin coating, thelayer formed by spin coating is preferably baked by vacuum heating. Forexample, an aqueous solution of poly(ethylenedioxythiophene)/poly(styrene sulfonic acid) solution (PEDOT/SS) may beentirely applied and baked to form a film that functions as a holeinjection layer. Then, a polyvinyl carbazole (PVK) solution doped with aluminescent center colorant (1,1,4,4-tetraphenyl-1,3-butadiene (TPB);4-dicyanomethylene-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran (DCM1);Nile red; coumarin 6; or the like) may be entirely applied and baked toform a film that functions as the light emitting layer.

The light emitting layer may be formed as a single layer. For example, a1,3,4-oxadiazole derivative (PBD) having electron transport propertiesmay be dispersed in polyvinyl carbazole (PVK) having hole transportproperties. Further, white light emission can be obtained by dispersingPBD of 30 wt % as an electron transporting agent and dispersing anappropriate amount of four kinds of colorants (TPB, coumarin 6, DCM1,and Nile red). In addition to the light emitting element from whichwhite light emission can be obtained as shown here, a light emittingelement which can provide red light emission, green light emission, orblue light emission can be manufactured by appropriately selectingmaterials of the light emitting layer.

Further, a triplet light emitting material containing a metal complex orthe like as well as a singlet light emitting material may be used forthe light emitting layer. For example, among pixels emitting red, green,and blue light, a pixel emitting red light whose luminance is reduced byhalf in a relatively short time is formed of a triplet light emittingmaterial and the rest are formed of a singlet light emitting material. Atriplet light emitting material has a feature of good luminousefficiency and less power consumption to obtain the same luminance. Whena triplet light emitting material is used for a red pixel, only a smallamount of current needs to be supplied to a light emitting element.Thus, reliability can be improved. A pixel emitting red light and apixel emitting green light may be formed of a triplet light emittingmaterial and a pixel emitting blue light may be formed of a singletlight emitting material to achieve low power consumption. Low powerconsumption can be further achieved by forming a light emitting elementwhich emits green light that has high visibility with a triplet lightemitting material.

A metal complex used as a dopant is an example of a triplet lightemitting material, and a metal complex having platinum that is a thirdtransition series element as a central metal, a metal complex havingiridium as a central metal, and the like are known. A triplet lightemitting material is not limited to the compounds. A compound having theabove described structure and an element belonging to any of the Groups8 to 10 of the periodic table as a central metal can also be used.

The above described materials for forming the light emitting layer arejust examples. A light emitting element can be formed by appropriatelystacking functional layers such as a hole injection transport layer, ahole transport layer, an electron injection transport layer, an electrontransport layer, a light emitting layer, an electron blocking layer anda hole blocking layer. Further, a mixed layer or a mixed junction may beformed by combining these layers. The layer structure of the lightemitting layer can be varied. Instead of providing a specific electroninjection region or light emitting region, modification such asproviding an electrode layer for the purpose or providing a dispersedlight emitting material is acceptable as long as it does not deviatefrom the scope of the present invention.

A light emitting element formed with the above described materials emitslight by being forward biased. A pixel of a display device formed with alight emitting element can be driven by a simple matrix mode or anactive matrix mode. In any event, each pixel emits light by applying aforward bias thereto at a specific timing; however, the pixel is in anon-light-emitting state for a certain period. The reliability of thelight emitting element can be improved by applying a reverse bias in thenon-light-emitting time. In the light emitting element, there is adeterioration mode in which emission intensity is decreased underspecific driving conditions or a deterioration mode in which anon-light-emitting region is enlarged in the pixel and luminance isapparently decreased. However, the progression of the deterioration canbe slowed down by alternating current driving where bias is appliedforward and reversely. Thus, the reliability of the light emittingdevice can be improved. Additionally, either of digital driving andanalog driving can be applied.

A color filter (coloring layer) may be formed over the sealingsubstrate. The color filter (coloring layer) can be formed by a vapordeposition method or a droplet discharging method. With the use of thecolor filter (coloring layer), high-definition display can also beperformed. This is because a broad peak can be modified to be sharp inlight emission spectrum of each RGB by the color filter (coloringlayer).

The case of forming a material displaying luminescence of R, Q; and B isshown above; however, full color display can be performed by forming amaterial displaying a single color light-emission and combining a colorfilter and a color conversion layer. The color filter (coloring layer)or the color conversion layer is formed over, for example, a secondsubstrate (a sealing substrate) and may be attached to the substrate.

Naturally, display may be performed with single color light-emission.For example, an area color type display device may be manufactured byusing single color light-emission. The area color type is suitable for apassive matrix type display portion, and characters and symbols can bemainly displayed.

In the above-mentioned structure, it is possible to use a low workfunction material as a cathode, for example, Ca, Al, CaF, MgAg, AlLi, orthe like is desirable. Any of a single layer type, a stacked type, amixed type having no interface between layers can be used for theelectroluminescent layer. The electroluminescent layer may be formed bya singlet material, a triplet material, or a mixture of the materials;or a charge injection transport material and a light emitting materialincluding an organic compound or an inorganic compound, which includesone layer or plural layers of a low molecular weight organic compoundmaterial, an intermediate molecular weight organic compound (which meansan organic compound having no sublimation properties, and the number ofmolecules is 20 or less or the length of linked molecules is 10 m orless), and a high molecular weight organic compound, which are definedby the number of molecules, and may be combined with an electroninjection transport inorganic compound or a hole injection transportinorganic compound. The first electrode layer is formed with atransparent conductive film which transmits light, and for example, atransparent conductive film in which zinc oxide (ZnO) of 2 to 20% ismixed in indium oxide is used in addition to ITO or ITSO. A plasmatreatment in an oxygen atmosphere or a heat treatment in vacuumatmosphere may be preferably performed before forming the firstelectrode layer. The bank (also referred to as a partition wall ormound) is formed with a material containing silicon, an organic materialor a compound material. Additionally, a porous film may be used.However, when a photosensitive material or a non-photosensitive materialsuch as acrylic or polyimide is used to form the bank, the side facethereof has a shape in which a radius curvature changes continuously,and an upper layer thin film is formed without disconnection due to astep, which is preferable.

According to the present invention, a highly reliable display device canbe manufactured through a simplified process. Therefore, a displaydevice that exhibits high-precision and high-quality images can bemanufactured at a low cost with high yield.

This embodiment mode can be freely combined with Embodiment Modes 1 to3.

Embodiment Mode 5

One mode in which protective diodes are provided for a scan line inputterminal portion and a signal line input terminal portion is explainedwith reference to FIG. 15. TFTs 501 and 502, a capacitor 504, and alight emitting element 503 are provided in a pixel 2702 in FIG. 15. ThisTFT has the same structure as that in Embodiment Mode 1.

Protective diodes 561 and 562 are provided for the signal line inputterminal portion. These protective diodes are manufactured in the samestep as that of the TFT 501 or 502 and are operated as diodes by beingeach connected to a gate and one of a drain and a source. FIG. 14 showsan equivalent circuit diagram of the top view shown in FIG. 15.

The protective diode 561 includes a gate electrode layer, asemiconductor layer and a wiring layer. The protective diode 562 has thesimilar structure. Common potential wirings 554 and 555 connecting tothe protective diode are formed in the same layer as that of the gateelectrode layer. Therefore, it is necessary to form a contact hole inthe insulating layer to electrically connect the common potentialwirings 554 and 555 to the wiring layer.

A mask layer may be formed and etching-processed to form a contact holein the insulating layer. In this case, when etching at atmosphericpressure discharge is applied, a local electric discharging process canbe performed, and the mask layer is not necessarily formed over theentire surface of the substrate.

A signal wiring layer is formed in the same layer as that of a sourceand drain wiring layer 505 in the TFT 501 and has a structure in whichthe signal wiring layer connected thereto is connected to the source ordrain side.

The input terminal portion of the scanning signal line side also has thesame structure. The protective diodes provided in an input stage can beformed at the same time. Note that the position of disposing aprotective diode is not limited to this embodiment mode and can also beprovided between the driver circuit and the pixel.

Embodiment Mode 6

A television device can be completed with a display device formedaccording to the present invention. A display panel can be formed in anymanner as follows: as the structure shown in FIG. 16A, only a pixelportion is formed, and a scan line driver circuit and a signal linedriver circuit are mounted by a TAB method as shown in FIG. 17B; as thestructure shown in FIG. 16A, only a pixel portion is formed, and a scanline driver circuit and a signal line driver circuit are mounted by aCOG method as shown in FIG. 17A; a TFT is formed of a SAS, a pixelportion and a scan line driver circuit are formed to be integrated overa substrate, and a signal line driver circuit is separately mounted as adriver IC as shown in FIG. 16B; a pixel portion, a signal line drivercircuit, and a scan line driver circuit are formed to be integrated overthe substrate as shown in FIG. 16C; or the like.

Another structure of an external circuit includes a video signalamplifier circuit which amplifies a video signal among signals receivedby a tuner; a video signal processing circuit which converts the signaloutput therefrom into a chrominance signal corresponding to each colorof red, green, and blue; a control circuit which converts the videosignal into an input specification of a driver IC; and the like on theinput side of the video signal. The control circuit outputs the signalinto the scan line side and the signal line side, respectively. In thecase of digital driving, a signal dividing circuit may be provided onthe signal line side, so that an input digital signal is provided bydividing into m-pieces.

Among signals received from the tuner, an audio signal is transmitted toan audio signal amplifier circuit, and the output thereof is suppliedfor a speaker through an audio signal processing circuit. The controlcircuit receives control information on a receiving station (a receivingfrequency) or sound volume from an input portion and transmits thesignal to the tuner or the audio signal processing circuit.

As shown in FIGS. 20A and 20B, a television device can be completed byincorporating a display module into a chassis. The display panel inwhich an FPC is attached as shown in FIG. 1 is generally called an ELdisplay module. An EL television device can be completed when the ELdisplay module as in FIG. 1 is used. A main screen 2003 is formed byusing the display module, and a speaker unit 2009, operation switches,and the like are provided as other attached equipments. In such amanner, the television device can be completed according to the presentinvention.

In addition, reflected light of light entered from exterior may beshielded by using a wave plate and a polarizing plate. In the case of atop emission display device, an insulating layer which is to be a bankmay be colored to be used as a black matrix. The bank can be formed by adroplet discharging method or the like, and a black resin pigment, aresin material such as polyimide, which is mixed with carbon black, orthe like may be used, or a stacked structure thereof may also be used.Depending on a droplet discharging method, different materials may bedischarged on the same region plural times to form the bank. Quarter orhalf wave plates may be used as wave plates and may be designed to beable to control light. As the structure, a TFT element substrate, alight emitting element, a sealing substrate (sealing material), waveplates (quarter or half wave plates), a polarizing plate are stacked inorder, in which light emitted from the light emitting element is emittedoutside from the polarizing plate side through the above components. Thewave plate or polarizing plate may be provided on a side where light isemitted or may be provided on the both sides in the case of a dualemission type display device in which light is emitted from the bothfaces. In addition, an anti-reflective film may be provided on the outerside of the polarizing plate. Consequently, a higher definition andhigher accurate image can be displayed.

As shown in FIG. 20A, a display panel 2002 using a display element isincorporated into a chassis 2001. By using a receiver 2005, in additionto reception of general TV broadcast, information communication can alsobe carried out in one direction (from a transmitter to a receiver) or inthe both directions (between a transmitter and a receiver or betweenreceivers) by connecting to a communication network by a fixed line orwirelessly through a modem 2004. The operation of the television devicecan be carried out by switches incorporated in the chassis or by aremote control device 2006, which is separated from the main body. Adisplay portion 2007 that displays information to be output may be alsoprovided in this remote control device.

In addition, in the television device, a structure for displaying achannel, sound volume, or the like may be additionally provided byforming a sub-screen 2008 as a second display panel in addition to themain screen 2003. In this structure, the main screen 2003 is formed ofan EL display panel superior in a viewing angle, and the sub-screen maybe formed of a liquid crystal display panel capable of displaying thesub-screen with low power consumption. In order to prioritize low powerconsumption, a structure in which the main screen 2003 is formed of aliquid crystal display panel, the sub-screen is formed of an EL displaypanel, and the sub-screen is able to flash on and off may be alsoapplied. According to the present invention, a display device with highreliability can be manufactured using such a large substrate even whenmany TFTs and electronic parts are used.

FIG. 20B shows a television device having a large display portion of,for example, 20 inches to 80 inches, which includes a chassis 2010, akeyboard 2012 which is an operation portion, a display portion 2011, aspeaker unit 2013, and the like. The invention is applied tomanufacturing the display portion 2011. FIG. 20B shows a televisiondevice having a curved display portion since a bendable material is usedfor the display portion. Thus, a television device having a desiredshape can be manufactured since the shape of the display portion can befreely designed.

According to the present invention, a display device can be manufacturedthrough a simplified process and thus the manufacturing cost can bereduced. Hence, even a television device with a large screen displayportion can be formed with low cost by applying the present invention.Accordingly, a high-performance and highly reliable television devicecan be manufactured with high yield.

Note that the present invention is not limited to the television deviceand is applicable to various usages especially to the display mediumshaving a large area such as an information display board at a station,an airport, or the like, or an advertisement display board on the streetas well as a monitor of a personal computer.

Embodiment Mode 7

Various display devices can be manufactured by applying the presentinvention. In other words, the present invention can be applied tovarious electronic devices in which these display devices areincorporated into display portions.

The electronic devices include a camera such as a video camera or adigital camera, a projector, a head mounted display (a goggle typedisplay), a car navigation system, a car stereo, a personal computer, agame machine, a portable information terminal (a mobile computer, acellular phone, an electronic book, or the like), an image reproducingdevice provided with a recording medium (specifically a device that iscapable of playing a recording medium such as a Digital Versatile Disc(DVD) and that has a display device that can display the image) or thelike. FIGS. 21A to 21D show the examples thereof.

FIG. 21A shows a computer, which includes a main body 2101, a chassis2102, a display portion 2103, a keyboard 2104, an external connectionport 2105, a pointing mouse 2106 and the like. According to the presentinvention, a computer by which an image with high reliability and highresolution can be displayed can be completed even if the computer isminiaturized and a pixel becomes minute.

FIG. 21B shows an image reproducing device provided with a recordingmedium (specifically a DVD player), which includes a main body 2201, achassis 2202, a display portion A 2203, a display portion B 2204, arecording medium (such as a DVD) reading portion 2205, operation keys2206, a speaker portion 2207 and the like. The display portion A 2203mainly displays image information and the display portion B 2204 mainlydisplays character information. According to the present invention, animage reproducing device by which an image with high reliability andhigh resolution can be displayed can be completed even when the imagereproducing device is miniaturized and a pixel becomes minute.

FIG. 21C shows a cellular phone, which includes a main body 2301, anaudio output portion 2302, an audio input portion 2303, a displayportion 2304, operation switches 2305, an antenna 2306 and the like.According to the present invention, a cellular phone by which an imagewith high reliability and high resolution can be displayed can becompleted even when the cellular phone is miniaturized and a pixelbecomes minute.

FIG. 21D shows a video camera, which includes a main body 2401, adisplay portion 2402, a chassis 2403, an external connection port 2404,a remote control receiving portion 2405, an image receiving portion2406, a battery 2407, an audio input portion 2408, an eyepiece 2409,operation keys 2410 and the like. According to the present invention, avideo camera by which an image with high reliability and high resolutioncan be displayed can be completed even when the video camera isminiaturized and a pixel is minute. This embodiment mode can be freelycombined with the above embodiment modes.

EXAMPLES Example 1

As for the etching process for forming an opening in the secondinterlayer insulating layer used in the present invention, an experimentis carried out changing etching conditions. The experimental results areshown below.

A sample is formed as follows: a source or drain electrode layer and asecond interlayer insulating layer are formed, a mask of resist isformed thereover and etched to form an opening reaching the source ordrain electrode layer in the second interlayer insulating layer, asdescribed in Embodiment Mode 1. A titanium film is formed as the sourceor drain electrode layer and a silicon oxide film containing an alkylgroup with a siloxane resin is formed by a coating method as the secondinterlayer insulating layer. A mask is formed for patterning and etchingis conducted under nine etching conditions A to I. SEM photographs ofthe openings after etching by a scanning electron microscope are shownin FIGS. 22A to 22I. The state of residue that remains in the bottom ofthe opening is evaluated with three levels. The sample having no residueis shown by Level 1, the sample having less residue is shown by Level 2,and the sample having much residue is shown by Level 3. Each conditionand each level of the residue is shown in Table 1.

TABLE 1 Power Gas flow rate ICP Bias Pressure CF₄ O₂ Condition (W) (W)(Pa) (sccm) (sccm) Residue level A 3000 2000 1 120 280 3 B 5000 3000 1180 220 1 C 7000 4000 1 240 160 1 D 3000 3000 3 240 160 2 E 5000 4000 3120 280 3 F 7000 2000 3 180 220 2 G 3000 4000 5 180 220 2 H 5000 2000 5240 160 2 I 7000 3000 5 120 280 3

As apparent from FIGS. 22A to 22I and Table 1, in the sample inCondition B, a favorable opening having no residue can be formed.Moreover, as the second interlayer insulating layer, a two-layer stackedstructure of a silicon oxynitride film and a silicon oxide filmcontaining an alkyl group is formed, and the titanium film, the siliconoxynitride film and the silicon oxide film containing an alkyl group arestacked to form a sample. A mask of resist is formed in the sample andan opening to reach the titanium film is formed by etching. Each etchingis conducted under eight etching conditions J to Q. Like the abovedescribed experiment, each condition is shown in Table 2 and SEMphotographs of the openings after etching are shown in FIGS. 23A to 23H.

TABLE 2 Power Gas flow rate ICP Bias Pressure CF₄ O₂ Condition (W) (W)(Pa) (sccm) (sccm) J 5000 3000 1 180 220 K 5000 3000 0.8 180 220 L 50003000 1 240 160 M 5000 3000 0.8 240 160 N 5000 4000 0.8 240 160 O 70004000 0.8 240 160 P 7000 2000 0.8 240 160 Q 7000 1000 0.8 240 160

As apparent from FIGS. 23A to 23F, in the samples in Condition O, P andQ, favorable openings having less residue can be formed. As theexperimental results, the selectivity of the titanium film and thesilicon oxide film containing an alkyl group depends on a gas flow ofCF₄ and O₂, and there is a tendency that the selectivity is enhanced byincreasing the O₂ flow rate. Similarly, the selectivity of the siliconoxide film containing an alkyl group with a siloxane resin and thesilicon oxynitride film depends on a gas flow of CF₄ and O₂, and thereis a tendency that the selectivity is enhanced by increasing the O₂ flowrate. The uniformity of etching rate of the silicon oxide film includingan alkyl group with the use of a siloxane resin depends on a pressure,and the pressure is made low and high vacuum is made to increase theuniformity. The residue due to an etching defect in the openings dependson the pressure and the flow rate of CF₄ and O₂, the pressure is madelow to make high vacuum and the flow rate of CF₄ is reduced, therebyreducing the residue. In consideration of the above, an etchingcondition can be set. An opening having superior flatness that canobtain a favorable contact of the first electrode layer, and the sourceand drain electrode layer can be formed through a simplified process.

Example 2

Insulating films for forming a display device are formed continuouslyand an evaluated result of an interface state therebetween is shown inExample 2.

In Example 2, as an insulating film, a silicon nitride oxide (SiNO) filmis formed as a first insulating film, and a silicon oxynitride (SiON)film is stacked thereover as a second insulating film. The first andsecond insulating films are formed continuously by changing reactivegases at the same temperature of 330° C. while keeping the vacuum(without breaking the vacuum) in the same chamber.

In Example 2, over a glass substrate, a silicon nitride oxide (SiNO)film of 200 nm thick is formed with each gas flow of SiH₄ of 80 sccm,NH₃ of 750 sccm, H₂ of 400 sccm, N₂ of 400 sccm, N₂O of 60 sccm as areactive gas; the pressure of 65 Pa; the frequency of 18.56 MHz; and thepower of 730 W. Then, a silicon oxynitride (SiON) film of 800 nm thickis formed continuously with each gas flow of SiH₄ of 75 sccm, N₂O of1200 sccm as a reactive gas; the pressure of 70 Pa; the frequency of13.56 MHz; and the power of 120 W. After that, the films are taken intothe air and an amorphous silicon (a-Si) film is formed as a cap film forprotection, with each gas flow of SiH₄ of 220 sccm and H₂ of 220 sccm asa reactive gas; the pressure of 160 Pa; the frequency of 13.56 MHz; andthe power of 160 W.

The samples in which SiNO, SiON and a-Si are in order stacked over theglass substrate are analyzed using a SIMS (secondary ion massspectrometry). As the stacked layer of SiNO and SiON, the interfacestate of the stacked layer and the impurity concentration (H, C, N, O,F) included in each film are measured. The measurement results are shownin FIGS. 24 to 26. FIG. 24 shows data quantified by Si standard sample,FIG. 25 shows data quantified by SiO₂ standard sample, and FIG. 26 showsdata quantified by SiN standard sample.

As the SiNO film, the hydrogen concentration is 1.8×10²² atoms/cm³, thecarbon concentration is 2.0×10¹⁷ atoms/cm³, the oxygen concentration is7.4×10²¹ atoms/cm³, and the fluorine concentration is 1.8×10²⁰atoms/cm³. As the SiON film, the hydrogen concentration is 2.5×10²¹atoms/cm³, the carbon concentration is 2.7×10¹⁸ atoms/cm³, the nitrogenconcentration is 2.3×10²¹ atoms/cm³, and the fluorine concentration is4.4×10²⁰ atoms/cm³. As the a-Si film, the hydrogen concentration is3.5×10²¹ atoms/cm³, the carbon concentration is 2.9×10¹⁸ atoms/cm³, thenitrogen concentration is 6.7×10¹⁹ atoms/cm³, the oxygen concentrationis 4.2×10¹⁸ atoms/cm³, and the fluorine concentration is 6.0×10¹⁸atoms/cm³.

As apparent from FIGS. 24 to 26, the interface impurity concentration ofthe SiNO film and the SiON film do not show a pileup phenomenon causedby high concentration impurities due to contamination. Thus, it isobserved that the interface state is favorable. In addition, it is notobserved that a component of the reactive gas (such as NH₃) used informing the SiNO film is diffused into the SiON film. Therefore, it isconfirmed that insulating films can be formed with a favorable interfacestate without contamination of the interface, when the insulating filmsare continuously stacked in the same chamber without being exposed tothe air. When such insulating films are used as one component forforming a display device, the reliability of the display device can beenhanced.

1. (canceled)
 2. A semiconductor device comprising: a pixel portioncomprising a transistor and a light emitting element electricallyconnected to the transistor, the transistor comprising: a semiconductorlayer; a gate electrode over and overlap the semiconductor layer; andsource and drain electrodes over and electrically connected to thesemiconductor layer; and a protective circuit, wherein the semiconductorlayer comprises a region which does not overlap any of the gateelectrode, the source electrode, and the drain electrode, wherein a partof a gate wiring layer functions as the gate electrode, wherein the gatewiring layer comprises a first portion in the pixel portion and a secondportion in the protective circuit, wherein the first and second portionsextend along the same direction, and wherein the first and secondportions do not extend in the same straight line.
 3. A semiconductordevice comprising: a pixel portion comprising a transistor and a lightemitting element electrically connected to the transistor, thetransistor comprising: a semiconductor layer; a gate electrode over andoverlap the semiconductor layer; and source and drain electrodes overand electrically connected to the semiconductor layer; and a protectivecircuit between the pixel portion and a driver circuit, wherein thesemiconductor layer comprises a region which does not overlap any of thegate electrode, the source electrode, and the drain electrode, wherein apart of a gate wiring layer functions as the gate electrode, wherein thegate wiring layer comprises a first portion in the pixel portion and asecond portion in the protective circuit, wherein the first and secondportions extend along the same direction, and wherein the first andsecond portions do not extend in the same straight line.